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Feature Updates

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3.7 | 3.6.1 | 3.6 | 3.5.1 | 3.5 | 3.4.1 | 3.4 | 3.3 | 3.2.1 | 3.2 | 3.1.1 | 3.1 | 3.0.2 | 3.0.1 | 3.0 | 2.1.5 | 2.1.4 | 2.1.3 | 2.1.2 | 2.1.1 | 2.1 | 2.0.3 | 2.0.2 | 2.0.1 | 2.0 | 1.9.5 | 1.9.4 | 1.9.3 | 1.9.2 | 1.9.1 | 1.9 | 1.8.3 | 1.8.2 | 1.8.1 | 1.8 | 1.7.1 | 1.7 | 1.6.2 | 1.6.1 | 1.6 | 1.5.1 | 1.5 | 1.4.3 | 1.4.2 | 1.4.1 | 1.4 | 1.3.1 | 1.3 | 1.2 | 1.1 | 1.0.3 | 1.0.2 | 1.0.1 | 1.0

May 23, 2024 - Stella 3.7

Box and whisker graphs (video)

Box and whisker graphs allow you to show uncertainty over a series of realizations of an uncertain value. They, importantly, allow comparative display across different uncertain scenarios when set up across array elements as described in Box and Whisker Graph. Learn more

Confidence graphs (video)

Confidence graphs allow you to see the spread of outcome across either multiple runs or multiple array elements.

Models that had comparative line graphs set up with the option to plot confidence values will automatically be translated into the new graph type. The option to plot confidence values no longer appears on the line graph. Learn more

Correlation graphs (video)

Correlation graphs allow you to see the relationship over time of different variables across sensitivity runs. This is a an effective way to explore the important determinants of behavior for selected variables. Learn more

More control over line graph appearance

In addition to numbers, you can also mark graph lines with letter and symbols. See Line Graph for details. The Correlation Graph also supports this.

The Line Graph also has a new option to draw series with stepwise connections between points, so that the graph lines consists only of horizontal and vertical segments with no interpolation between them. See Graph Series Property Panel for details.

Graph selection from dropdown

Rather than selecting graph types by clicking on a radio button, they are now selected from a dropdown list of types. This makes it easier to see which types of graph you will be adding. Learn more

CLD generation based on tags (video)

To create a CLD from a set of tagged variables simply click on CLD View in the Mode Toolbar. This will bring up the CLD Tag Selection dialog box which will allow you to specify which tags to use. The resulting CLD is the same as those created using Loops that Matter as discussed in CLD Generation.

Selecting array elements to display (video)

Tables and graphs, including the Results Panel, allow you display all elements of an array together. For large arrays this can be cluttered, and the new Array Selection Panel allows you to select which elements of an array you would like to see values for.

Improvements to arrayed equations (video)

Version 3.7 contains a number of changes that make it easier to work with arrayed variables and their equations.

A CONTAINS keyword has been added that provides a quick way of testing whether the current element in an array is contained in a subrange of the array. This can simplify equations that might depend on nested IF THEN ELSE to do these tests, and also improves maintainability. See Subranges for more discussion.

Non Apply-To-All (a2a) equations now allow the use of dimension names in equations, making it easier to set multiple entries to the same equation. See Creating Arrayed Variables and Arrayed Equation editing dialog for more details.

Filling in new array elements

An option has been added to the Array Editor dialog box to duplicate array elements. This allows the expansion of arrays by replicating non a2a equations from the specified source (for example repeating a constant value). See also the Array Element Duplicate dialog box.

Graphical improvements (video)

Graphicals now have an option to repeat changes made to a y value for all following y values when changing values in a table as described in Graphical Function Tab. This makes it easier to change a number of values at once, especially on the interface.

The Graphical input (Interface) has also been extended to allow control over how the dialog first displays (graph or table) and whether the interface user can switch between them.

Color palettes for global graph styles (video)

We have added some useful color pa lattes to the Global Graph Styles Properties Panel. This makes it easier to change the sequence of colors displayed in graph. Learn More

Sensitivity and optimization selection on the interface (video)

When selecting sensitivity or optimization as a button, it is now possible to select which sensitivity or optimization specifications to use. Learn More

Improvements to the Parameter Control Window (video)

The Parameter Control Panel now allows you to reorder the entries and keep them in place as you reset inputs and after saving and reopening a model. This makes it much easier to keep track of changes that are being made in the current run.

It is also possible to control graphicals directly from this panel, in addition to controlling them from the Results Panel. This makes it possible to temporarily change a graphical without entering Stella Live or using the interface, and also keeps all the changes in one place.

Setting variable colors by tag (video)

The color and fill color displayed by variables can be set by tag from the Model Style Properties Panel. This allows you to customize your model appearance without changing individual variables and has the advantage that changing the tag for a variable from the Documentation Tab of the properties panel is all that is necessary to change its color.

April 4, 2024 - Stella 3.6.1

Explicit array ranges

The notation used in SUM in other array operations can now include dimension_name.* instead of just *. This removes ambiguity and allows more flexibility in operations involving differently arrayed variables. Learn More

Font selection for dropdown graph and table selection (Interface)

You can now set the font used in the dropdown for page selection of graphs and tables as described in Graph Styles Tab. Learn More

February 29, 2024 - Stella 3.6

Variable tags (video)

Tags are text you an attach to model variable using the Documentation Tab. They allow you to search for and select using the Find window, export using the Export Data dialog box, or omit from the Equation Viewer. They make it easy to group and organize variables in any number of ways to apply different characteristics such as number formatting.

Array element display label imports

When importing data from the interface (published or on the desktop) it is now possible to set the array element display labels using Import as described in Actions (Interface). This allows customization of the interface to reflect, for example, the country under study. Learn More

Specifying import files for the interface (video)

In addition to being able to import display labels, you can also provide files to be imported when a button is pressed as described in Actions (Interface). These files will be available when published and can be used to load data and array element labels for different interface configurations. Learn More

Full model navigation on interface (video)

When using the Model View object (or Storytelling) it is now possible to have the diagram be navigable between different modules. Double clicking on a module will open it, and there are up and home buttons for navigating to parent modules just as there are when editing models.

Ghosting of modules (video)

It is now possible to create ghosts of modules using the tool in the Model Build Toolbar. This allows you to decrease clutter in the diagram. Module ghosts can only be placed in the same model the module resides in (no cross-level module ghosts are allowed). You change connecters starting from the module to starting from a ghost of it by drawing the connector from the ghost. Similarly, it is now possible to move connectors starting from a variable and going into a module to start from a ghost of that variable by redrawing them. None of these changes have any impact on model structure and the dialog that used to appear asking if you want to continue is no longer shown. Learn More

More Find functionality (video)

The Find window now allows you to filter for constants, non-constants, unused variables, and module outputs used to create cross level ghosts. There is also an option to select based on Tags as noted above. Also, typing in a module qualified name will show all variables in that module in addition to cross-level ghosts. Learn More

On demand control imports

On demand imports defined in the Import Data dialog box can now be set to control values, rather than replacing equations. The controlled values are treated as user controlled, and will be marked this way in the Parameter Control Panel.

Improved graph and table pasting

Graphs and tables moved from one module in a model to another will retain their content regardless of the relative location of the variables being displayed. This allows copy and pasting of graphs and tables without having to ensure that cross-level ghosts are created to support the pasted content.

Run name cleanup (video)

When you save runs or lock runs in the Data Manager it no longer causes the run names to have increasingly large numbers. Instead, runs are named based on the number of active runs showing, with a check to be sure that the name is unique. If there are runs with numbers in the list the next run will have a number one larger. If the active runs do not have numbers, the next run will have the default number 1. Learn More

Opening data files as models (video)

It is now possible to open csv or txt files that are set up with import data as models. This is a convenient way to generate the variables necessary to support imports, and also to just look at data. These files are open from the File Menu just as models are, but will create a new model with the variables in the file and set up the import link so that you can look at values in Stella by running the model. You can also copy and paste the imported elements to other models if you only need to import a subset of the data. Learn More

Messages for binding non-negativity constraints

When Stella prevents a negative value in a uniflow, constrains outflows to keep a stock non-negative, or constrains inflows because of a capacity constraint in a conveyor it will highlight the associated variables in yellow. In addition to this highlighting, there will now be a dropdown in the Run Toolbar that will navigate to the constrained variables. There is an option in the Preferences Dialog to turn this off. It must also be turned off in the Model Settings Properties Panel for the model you are working with.

Fewer unnecessary file changes

Modules that are saved in separate files are now only written out if they have been changed. This is intended to make working on projects with a number of different contributors easier, as there will not be any changes made to module files that are not themselves changed. Learn more

Simpler array element naming

It is no longer necessary to use quotes for array elements that have special characters in them when editing in the Array Editor dialog box. The quotes will be added automatically when they are needed (for example in equations). Learn More

More control over table appearance

It is now possible to separately set alignment on the row and column table headers separately from the table cell alignment. Learn More

Native tooltips for buttons

An option to use the native tooltip has been added to the Button (Interface). Learn More

More control over gauge appearance

There is now an option to hide the units of measure in the Gauge (Interface). Learn More

More complete causes and uses navigation

The causes and uses entries on the Context Menu has been enhanced to show more clearly the module relationships for variables used in modules different from where they are defined. Learn More

December 14, 2023 - Stella 3.5.1

Display labels for array elements

Display labels for array elements permit the use of more descriptive text for array labels while allowing the labels used in equations to be shorter. Display labels will appear in graphs, tables, and input devices including the Selector when configured for array selection. They can include any characters and do not need to be quoted. Display labels are defined in the Array Editor dialog box, and can also be imported as discussed in Setting Up Import Links.

Better table labeling for arrays

When you are working with Tables and add an array using *, the table title will change to the name of the variable and the entries to the names of the array elements. This is the same way that graph labeling works. This is only used when the table has single arrayed variable and a * has been selected. Learn More

New builtins to simplify parametrization of nonlinear relationships

A number of new builtins have been added. LOGISTICBOUND allows the parametrization of a transition from one value to another following a logistic (s-shaped) pattern. EXPBOUND allows the parametrization of exponential adjustment from one value to another both convergent and divergent. The two together provide the same set of choices available as the preset shapes in the Graphical Function Tab. MINSOFT and MAXSOFT allow a smooth approach to a minimum or maximum value rather than the abrupt change that results from using MIN or MAX. These functions are described in more detail in Mathematical builtins.

In addition a SYSTEMCHANGE builtin has been added. This builtin returns the system change metric reported in the Loops Panel. Like PATHSCORE, it is computed after a run completes, so should not be used as an input to any other variable. For more detail see Specialized builtins.

Units search and other find functionality

The Find window now has an option to search in units. This is a convenient way to select everything that has the same units to either change the units, or change the appearance of the variables. The search functionality also allow search for empty values, which is most useful for finding variables without documentation, an equation or units - though the latter two are also shown in the toolbar. Learn More

Performance optimization

The software responsiveness when making changes in very large models has been improved. In addition, macro definitions that contain only converters are now expanded inline to decrease memory consumption and improve performance during simulations (for more on macros see Working with Macros).

Interface grid to improve object placement

There is now an option on the Interface Settings Properties Panel to show gridlines on the interface pages. You can specify the number of gridlines horizontally and vertically and they will appear in light gray in the background. These can be useful for aligning objects. Learn More

Imported time varying data no longer held constant when modules not running

When a variable has time varying data imported, it will also use the time varying values even if it is contained in a module or sector that is not being simulated. This makes it easier to perform partial model tests. See Partial Simulation Setup for information on simulating only parts of models. Learn More

Specialized builds

We are now making available specialized builds of Stella Professional and Stella Architect for older Macintosh operating systems and x64 Linux systems. These are built from the same source as the standard releases, but may have limitations on some functionality. Learn More

October 12, 2023 - Stella 3.5

Mapping Between Numbers and Text (video)

It is now possible to map specific numbers to words for both output and input. For example 0/1 can become Off/On. This is very helpful for presenting information, especially assumptions, in a readable way. These values will appear in graphs, tables, numeric displays and elsewhere. Working the other way, it is possible to enter words and have them be mapped to numbers in numeric inputs and other text based input devices, as well as the new drop-down input. For more information look at Manage Number-Text Mappings dialog box and Edit Number-Text Mapping dialog box opened through the Model Settings Properties Panel. Number-text mappings are added to variables in the in the Scales and Ranges Tab or the properties panel or from the Format Numbers dialog box or the Format Variable dialog box opened from the Context Menu on graphs, tables and other objects. It is also available on the Set Time Label Format dialog box allowing arbitrary text to be displayed for selected points in time. You can also set up default number-text mappings from the Default Settings Formats dialog and they will be available on new models that you create.

More Find and Replace Options and Persistence (video #1), (video #2)

You can now use the Find and Replace Dialog to replace text in equations in addition to modifying variable names and units. This can be very useful in adjusting array usage. The dialog content is also persistent, so when you close and reopen the model in an editing session the same selections will remain. Learn More

New Input Using a Drop-down List of Values (video)

The new Dropdown Input (Interface) allows you to specify a set of values that can then appear in a dropdown for selection by the user. This can be used most effectively when a Number-Text mapping has been specified for the variable being used. Learn More

Better Support for Changing Variable Dimensions (video)

Changing the dimensions of a variable will now update the places that variable is used more completely, including adding in or removing the dimension even when the variable was originally used without square brackets []. This makes it more likely the equations will remain valid, and less likely that an oversight (such as a SUM function with no []) will generate unexpected behavior.

Keep Excel Files Open (video)

There is now an option on the Preferences Dialog to keep Excel files open when they are referred to during import or export operations. This is most useful for Excel files that may show a dialog (for example do you want to update data) when they are opened. Learn More

Documentation Tab Changes (video)

The Documentation Tab icon will now change to show a green checkmark when there is content in the documentation. This makes it easier to know which variables have documentation written for them. Learn More

New Builtin Functions (video)

There are two new Builtins. The first is MATRIXINVERT which will give the inverse of a square 2 dimensional matrix or slice. This is a special array function as described in Array Operation builtins. The second, SOFTWAREVERSION is a convenience builtin to allow you to detect which version of the software is currently being used as described in Specialized builtins.

Import Template Provides More Options (video)

The Create Import Template dialog box now has an option to create a template only for selected variables, and also to create a time varying import template. Learn More

Find Persistence and Additions (video)

The Find window will now remember your last search settings and there is also an option to find imported values. Learn More

Import All and Export All Now Available as Menu Items (video)

New menu items have been added to the Model Menu to Import All and Export All. These are hand shortcuts with keyboard equivalent to import of export data without opening the respective dialogs. Learn More

Selecting Specific Columns or Rows When Copying Tables (video)

You can now select different rows or columns in a table to copy to the clipboard. Learn More

Specific Ranges Allowed in Conveyor Initialization (video)

When using arrays to initialize conveyors it is now possible to specify a range within the array so that the array size does not need to line up with the transit time. Learn More

More Flexibility in Managing Array Interdependencies

More of the cases where an equation uses a relative array position will now trace through each element allowing more complete control on these computations. Importantly, arrays that have a computed index values, and those using @ notation can now be combined with a relative index position.

Disable Scrubbing on Graphs

There is now an option on graphs to disable scrubbing that can be set from Graph Settings Properties Panel. This is useful for small graphs that would not be readable when scrubbing values. Learn More

Assembly Option to Add Only Ghost to Model for Some Variables

Using ghosts, it is now possible to set up an assembly so that the ghosts it uses are automatically connected to variables with the same name in the model. Learn More

July 19, 2023 - Stella 3.4.1

Documentation added to Connectors and Loop Labels

It is now possible to add documentation to connecters and loop labels. The documentation is entered using the Documentation Tab as it is for variables and will display on hover. When using the Model View object on the interface the documentation will display if the option to show documentation is chosen, though Loop Labels will always display their documentation.

Comparative Tables Grouped by Run

Comparative tables can now be grouped either by variable or by run making it easier to see all variables for a given run. Learn More

Removing Borders on Allocation Input

The Pie Chart and the Allocation Input (Interface) have a new option to keep or remove the borders between the displayed pie slices. This can help to remove clutter.

Styling of Tabbed Graphs, Tables, Group Input, and Array Input

You can now customize the appearance of the tabs used to switch between different graphs and tables (or variables for the Group Input). Learn More

Stricter Units Checking

A strict units checking option has been added. It is on by default unless changed in the Default Settings Run Specs dialog. This option will check for dimensioned variables being used in graphicals and builtins such as EXP. The option is set on the Model Settings Properties Panel.

Controlling Initial Stock Values in Stella Live

Stocks with constant equations can now have the initial value updated from the Results Panel when using Stella Live™. This makes it easier to experiment with initial conditions.

June 12, 2023 - Stella 3.4

Assemblies on the Exchange (video #1, video #2, video #3)

In addition to the built in Assemblies that are part of Stella it is now possible to upload Assemblies to the isee Exchange and use uploaded Assemblies by setting up a connection in the Preferences Dialog. See Assembly Exchange for more discussion.

New Sensitivity Capabilities (video)

Sensitivity runs can now set up criteria to terminate and dismiss runs based on payoff values. This allows, for example, the exploration of future behavior for all runs that match historic behavior sufficiently well. Runs that do not match are not included in the final set of reported runs. The criteria are set in the Sensitivity Termination Criteria dialog which is accessed from the Sensitivity Specs Panel.

When setting up sensitivity runs, it is also much easier to add multiple sensitivity parameters at once. By using the new multiselection functionality of the Find window as described below, you can add a number of different parameters together. When adding more than one parameter the Multiple Range Specification dialog will open allowing you to specify the minimum and maximum values as a proportion of the base parameter value.

There is also a new sensitivity method that samples the sensitivity parameters sequentially. This is useful for going through a large number of parameters quickly to see which have significant impact in isolation. This is set in the Sensitivity Specs Panel.

Multiple Selections for Sensitivity and Optimization (video)

When adding variables to sensitivity or optimization specs you can now select multiple variables to add at once. This is done in the Find window which has an OK and Cancel buttons when multi selection is supported.

If you select arrayed variables you will get be able to select which array elements to use. Learn More

Improved Module Pasting (video)

If you paste a module and it is not possible to make all of the cross level connections between variables with the existing connectors new ones will be added to be able to make the connections. Cutting and pasting a module in a model will thus rewire all of the cross level connections as required. Invalid connectors from a module to a cross level ghost may also be removed to accommodate this.

Related to this, the error message for connectors into modules that do not have a cross level connection have been improved. The connector causing the error will now be highlighted when selecting the error message from the Run Toolbar. Learn More

Controlling Array Slices (video)

In addition to controlling variables you can now control a slice of a variable. This is useful when you want to set a default value for all elements, then override specific elements with other values. To do this use a * appropriate position in the Choose Subscript dialog box. Array slices can be used in any of the controls on the interface (except the Allocation Input) and also on the Parameter Control Panel for the model. Specific element controls will take precedence.

Filtering of Imports for Parameter Control Window (video)

The Parameter Control Panel now has an option to filter out imported variables. This makes it easier to see which model variables have been controlled using Stella Live, the interface, optimization or directly from the panel itself. Learn More

Non A2A Graphical Editor (video)

When working with graphicals that are not apply-to-all there is now an option to open the Arrayed Graphical editing dialog. This allows you to select multiple elements of the array and edit the graphicals for them together. Learn More

Hiding Thumbnails on the Interface Page (video)

The Preferences Dialog now has an option to hide thumbnails on the Interface Settings Properties Panel. Instead of a thumbnail just the page names will be displayed. This can simplify working with interfaces containing a large number of pages.

Pasting Variable Starts Name Editing

When you paste a variable into a model you can simply start typing to change the name - there is no longer any need to select the name first.

Highlight Point to be Moved in Graphical Editor

As you move the pointer inside of the Graphical Function Tab the point that will be moved by a click is highlighted making it easier to see what will happen. Learn More

More Intuitive Run Behavior when Switching out of Stella Live (video)

If you switch out of Stella Live by using the Stop Stella Live command on the interface or switching to edit mode on the model and make a run, the next Stella Live run will reuse the run number for that run. This prevents duplicate runs with the same result appearing.

Clearer Marking of Invalid Graphicals (video)

When you add elements to a non apply-to-all graphical array the missing elements will be highlighted rather than contain a default graphical.

Results Panel Highlight on Hover (video)

When you hover over a variable on the legend of the Results Panel the associated graph line will be highlighted. Learn More

Reorder Array Elements

You can now drag to reorder array elements in the Array Tab rather than having to delete and add them. Learn More

Binary Data Files (Stella Enterprise only)

There is now an option to store model runs in a binary format. This is intended for very large models and can be set model by model in the Data Manager. Learn More

Comma Decimal Command Prompt (Stella Simulator only)

There is a new command line option -cds to write to export data using , as the decimal delimiter. Learn More

March 15, 2023 - Stella 3.3

Optimization on the Interface (video)

It is now possible to run optimizations on the interface. To do this the optimization is first set up on the model as described in Optimization and Calibration and then executed on the interface using Run Optimization as described in Actions (Interface).

Optimization and Sensitivity Status Display

The Display Time (Interface) object now has an option to show the progress on sensitivity and optimization runs. This is a convenient way to let users know that work is being done in the background. Learn More

Selectors Active During Optimization

When using a Selector for either a placeholder or array dimension you can now change the value of the selector while an optimization is running. You can also double click on a minimized graph or table without stopping the optimization. Learn More

Tracing Optimization Overflows (video)

When there are divide by 0 or other overflows during an optimization there is now an option to stop the optimization with the value generating the error preserved to understand why it happened. This can be set on the Optimization Specs panel when running Powell optimizations as described in Optimization Methods.

Improved Zoom (video)

Zoom is now based on selected content, making it easier to select and then zoom in on a particular area in a model.

Connector Setting Added to Model Styles (video)

You can now set the thickness and polarity font for all connectors in a model in addition to changing specific connectors. Learn More

Allow Updating of Multiple Formats in Tables and Graphs (video)

When using the Format Numbers dialog box an Apply button has been added that allows you to make changes to multiple number formats without having to reopen the dialog. Learn More

Group Inputs Now Work with Placeholders and Wildcards

You can now use placeholders and wildcards in the Group Input (Interface) just as you can with other input and output objects. Learn More

Better Array Editing Messages

In the Array Editor dialog box dimension names that conflict with a model variable or builtin function (dimension names need to be globally unique ) will now put up a dialog letting you know there is a conflict. Learn More

Improved Diagram Rendering

Models with long runs and noisy data should render more quickly with Stella Live and in Suggest View improving usability.

January 13, 2023 - Stella 3.2.1

Expandable Scale Option on Graphs (video)

Graphs now have an option to rescale if the specified bounds are exceeded. This is useful for setting bounds that are usually right, but still having the graphs display all information when they are exceeded. Learn More

Sliced Graphs (video)

Sliced graphs allow you to overlay value from different time periods (most commonly years) for a single variable to see how one period compares with another. Learn More

Exporting, Importing and Duplicating, Sensitivity, Payoff and Calibration Specs (video)

To make it easier to move definitions between models, and to duplicate specs and make modifications Import, Export and Duplicate button have been added in the Sensitivity Specs Panel, the Payoff Specs panel and the Optimization Specs panel.

Simplified Calibration Payoff Setup (video)

The Payoff Specs panel has been updated to make setting up calibration payoff much simpler. Learn More

Scientific Notation in Formatted Numbers (video)

Scientific notation has been added as an option when formatting numbers and is set in the Scales and Ranges Tab of the properties panel. Learn More

Graphical Input Axis Labeling on the Interface

Graphical inputs on the interface can now have axis labels specified in the Graphical input (Interface) panel. Learn More

Easier Export File Creation (video)

You can now add a file for export without having to first create it. Learn More

Extending Percentile Builtin

The PERCENTILE builtin can now take an optional fourth argument which makes it possible to find the percentile value of an attribute based on volume (for example median age based on population). Learn More

Selecting Identically Arrayed Variables (video)

A new option has been added to the Context Menu on the model that allows you to select all variables arrayed the same way as the selected variable, making it easier to manipulate arrays. Learn More

November 17, 2022 - Stella 3.2

Assemblies (video #1, video #2)

Assemblies provide a new way to get started building models and easily add commonly used structures into ongoing modeling work. They work with suggested completions that fill in equations when possible or make suggestions based on the structure as you have drawn it. Learn More

Suggested Completions (video)

Suggested completions smooth the addition of simple equations based on the connections you make on the model diagram. They are turned on and off from the Mode Toolbar and are very helpful when working with Assemblies. Details on the way suggested completions work are in Completion Support.

Multiple Selections and Arrays Slices in the Results Panel (video)

The Results Panel has been extended to work with multiple variables and also has the ability to show all elements on an arrayed variable. This makes it very easy to see two or more variables next to one another to aid understanding and debugging model behavior. Learn More

Variable Replacement (video)

When there are two variables that have the same meaning it is now straightforward to replace one with the other without needing to edit equations, graphs, or tables by dragging one on top of the other. This is very helpful when combining assemblies. Learn More

Export of Multiple Runs from Interface (video)

An option has been added to export values from multiple runs on the interface making it easier to provide comparative summaries of different experiments conducted by published simulation users. Learn More

Flipping Parts of Diagrams (video)

There is now a function to flip the selected elements of a diagram either horizontally or vertically. This is accessed through the Context Menu. Learn More

Improved Units Suggestions (video)

The suggest units functionality - from either the Equation Tab of the properties panel or the Units Entry Popup will now look at both the equation for a variable, and equations using a variable, to try to determine the best units to suggest. When it is possible, units are also set automatically while working in Suggest view.

Improved Builtin Organization

The categories builtins are put into have been reorganized - in both the software and the help. See Builtins for the organization and Equation Tab for selecting them in the software.

Saving Diagrams to Images (video)

The Save As menu on the File Menu will now allow you to save the current module picture as a vector (pdf, svg) or raster (png, jpg, gif, bmp) image file. Learn More

New AGECOUNT Builtin

The AGECOUNT builtin provides a convenient way to look inside conveyors and queues (as well as non-negative stocks when using cycle time integration) returning the quantity of material falling within an age rate. Learn More

New Leakage Option

For conveyors with inflows that at spread evenly or based on a distribution there is now an option on linear leakage to leak the specified fraction of material regardless of the time the material spends in the conveyor. Learn More

October 7, 2022 - Stella 3.1.1

New Shortest Path Builtins

The new builtin SHORTESTPATH will compute the traversal sequence that will minimize the cost of getting from 1 node to another for a given adjacency matrix - where cost can be in distance, time or dollars. There is a corresponding builtin TRAVERSALCOST that computes that cost of such a path (or any path) through the adjacency matrix. Learn More

Add Ending and Beginning Options to Find and Replace

The Find and Replace Dialog now has an option to change only the beginning or ending of variable names. Learn More

Include Polarities from Vensim Models

If you open a Vensim model with polarities on the connectors those will now be brought across to Stella.

September 2, 2022 - Stella 3.1

Measuring System Movement in LTM (video)

A new measure of activity during a simulation is now available to make it easier to understand which loops are driving behavior during periods of significant change. The System Change and Contributions are on the Loops Panel and there is more discussion of the concepts in the Loops That Matter™ Overview.

Displaying Sums Across Arrays in Tables and Graphs (video #1, video #2)

When you select an arrayed variable for use in a table, graph, or other output object you can ask to display the sum, min, max or mean across a slice of the array in addition to specific array elements. See Choose Subscript dialog box for the details of doing this.
It is also possible to set up array definitions so that the sum, min, max, and mean can be selected when using a Selector or looking at values in the Results Panel. These are specified in the Dimension Configuration dialog box.

Find and Replace (video)

There is now find and replace functionality that allows you to change the names of all variables in a selection, or for the entire model. Use Shift+Ctrl+F or Ctrl+H (Windows)/Shift+⌘+F (Macintosh) to open the Find and Replace Dialog.
To be consistent with most other applications the Find (and Find and Replace) functionality is on the Edit Menu, and not on the Model Menu as it used to be.

Time Range in Tables (video)

You can now optionally specify a start and stop time for tables. This makes it possible to show value for a subset of a runs range. Learn More

Navigate on Undo/Redo

When using Undo (Ctrl+Z/⌘+Z) or Redo (Ctrl+Y/⌘+Y) the thing that was changed will not be highlighted (navigating to the appropriate module or page if necessary) and the associated panel open when one thing was changed. In some cases, because of cascaded dependent changes or changes applied to multiple selections, it may not be possible highlight anything.

Equation Editor Improvements

The autocomplete function now works even when there is no space after the cursor. In addition, selecting [ when inside an existing [] pair will replace the content inside the [] with whatever is provided by the Choose Subscript dialog box.

Multi Selection Panels (video)

More properties can be set on the panel when multiple objects are selected. For example when working on the interface you can select multiple sliders and set the ranges on all of them at the same time. Learn More

Flow Valve Resizing (video)

Flow valves can now be resized just as other building blocks can. The Model Style Properties Panel now allows the default size of flow valves to be set separately (they used to be the same as converters) as does the Default Settings Diagram dialog.

Modelview and Story Content Positioning (video)

It is easier to position content in Model View objects (including Storytelling pages) using arrow keys.

New Builtin

There is a new builtin NORMALPINK (see Statistical builtins) that can be used to generate correlated noise and simplifies opening of Vensim models.

July 5, 2022 - Stella 3.0.2

New Builtins

A number of new builtins have been added, and others extended to provide more behavior.

The new RUN builtins RUNCUM, RUNMAX, RUNMEAN, and RUNMIN make it easy to pull values of a variables from the current run, or from other runs much like the HISTORY builtin. It is also possible, when using time varying imports (Import Data dialog box) to pull future values for the current run. Learn More

The new LOOKUP builtings LOOKUPMIN and LOOKUPMAX make it easy to find the maximum or minimum in a graphical. The existing builtins LOOKUPAREA and LOOKUPMEAN have also been extended to take a variable number of arguments to simplify equation writing. Learn More

The STEP builtin now takes optional arguments for duration and interval maxing it easy to create a temporary step, or a repeating step. Learn More

Using Dimensions to Restrict Outflows

When restricting outflows from queues to content with certain attributes you can now use a dimension name in addition to numbers to specify which attributes to filter on. This is a convenient way of dispatching from an non-arrayed queue to arrayed stocks. Learn More

Using Arrays in Sensitivity Setup

It is now possible to specify arrays for parameters when setting up sensitivity. This makes it easier to specify a number of parameters, and to change array sizes without having to modify the sensitivity settings. Learn More

Better Vensim® Model Translations

The translation of Vensim models with multiple views now breaks the model up into modules and those the interconnection between the modules on the top level model. This makes it easier to work with larger models. Learn More

Importing External Run Data into Modules

When importing data as a run from the Data Manager using the Load External Data dialog box there is now an option to match unqualified names to variables within modules. This is useful when the data files list variable without module qualifications as might happen with values exported from a Vensim model.

Updated Panel Buttons

The ^ panel button has been replaced with [ to make it easier to work with arrays. Learn More

Exporting Results from the Interface

When exporting results from the interface the user will now be prompted for the name to export to. Learn More

Setting Arrays on Flows

Outflows from non-arrayed stocks can now have arrays set.

May 23, 2022 - Stella 3.0.1

Stella Live on Graphical Change

Now when you make graphical changes in the Graphical Editor dialog box Stella Live will update the module results as you make changes to the graphical. If you uncheck the option for "Stella Live update on drag" in the Model Settings Properties Panel changes will not be applied until you click on the OK button.

Scales and Ranges Settings Inherited for Sensitivity and Optimization

The minimum and maximum set in the Scales and Ranges Tab are now used automatically when adding a variable in the Sensitivity Specs Panel or Optimization Specs.

Lock Icon Changed to Tooltip

The lock icon that appeared in the upper right corner of objects locked on the interface has been replaced by a tooltip that indicates the object is locked. Double click or right-click and select unlock from the menu to edit a locked object.

April 14, 2022 - Stella 3.0

Interface by Design

We have dramatically simplified the process for building high quality interfaces by providing a number of Designs that you can bring into your interface and then customize. See the overview in Building Interfaces as well as the discussion in Designs. You can even create your own Designs from the Interface Menu (Interface) or by saving an Interface to the Custom Design directory specified in the Preferences Dialog.

Check out the quick tutorial on our tutorials page.

Interface Templates and Locks

You can directly edit content on Templates by double clicking on it from an Interface page. Right clicking will also take you to the Template page. Locked content will now display a lock icon in the upper right corner (right-click to unlock). Learn More

New Shapes

A number of new shapes have been added for display on the interface, including arrow, star, ellipse, cloud, and speech bubbles. You can also put a corner radius on rectangles. Learn More

Web Safe Fonts

To improve consistency in publication there is now an option (on by default) to use font faces that are available on almost all computers. Selecting fonts from the smaller list will make interface users see the same thing you do. The option is set in the Preferences Dialog. Learn More

Better Page Resizing on the Interface

Changing the Interface page size will now scale all content to the new size. Learn More

Interface Page Descriptions

You can now add a description to each interface page. The descriptions display when you hover over the page in the Pages Panel (Interface). You set the description in the Interface Settings Properties Panel.

Placeholder and Array Selection on the Model

You can now put Selector controls directly onto the model diagram. This makes it convenient to go through placeholders or array elements in graphs and tables. Learn More

More SVG Graphics Support

You can now use SVG files in the Graphics box, Button (Interface), and other places that take images.

Discrete Optimization

There is a new option for discrete optimization that allows you to find optimal values that are integers or otherwise quantized. Learn More

Improved Navigation Control Styling

The Navigation Control (Interface) now provides more options on appearance and layout including spacing between tabs and padding of text within them. The naming conventions used in the panel have also be simplified. Learn More

More Control over Numeric Displays

You can now set the label position and control the border and appearance more precisely for Numeric Displays as detailed in Numeric Display Properties. In addition, numeric displays on the model and interface now look the same. Learn More

Tooltips for Buttons and Annotations

You can now add tooltips to Button (Interface) that will display with the user positions the cursor over the button. In addition. Annotation Button (Interface) can be configured to display when the mouse moves over its button rather than requiring the user to click on the button.

Run Name Control

You can now set the run name in the interface using the Button (Interface).

It is also possible to set the beginning of the run name in the Model Settings Properties Panel. Using this instead of Run1, Run2, and so on you can have Test1, Test2, or another prefix displayed on tables and graphs.

In additions, for sensitivity runs that are specified using an external file you can include the run name in addition to parameter values. This makes it easy to name the runs according to their inputs (Low, Medium, High and so on). For details see the Sensitivity panel.

Arrays in Tables

Tables now allow the use of a * to represent all elements of an array that will update when the array definition changes. Learn More

Graphics Frame Transparency

There is now a transparency setting on Graphics Frames (interface only). This makes it easier to achieve different visual effects. Learn More

More Control in Run by Module

The options to run by module now allow you to turn on and off nested modules when you change the running state of a module on both the model and interface. This is done in the Partial Simulation Setup panel.

The software will also keep track of changes made to which modules are running on the interface and continue to run only those modules on the model until inputs are restored or the modules are switched on or off directly. Learn More

Better Control of Find

You can now search for exact matches in the Find window by using "" around a string, as well as names that start or end with something. Starting and ending spaces are also recognized to simplify looking inside of names. Learn More

Improved Cross Level Marking

It is now straightforward to mark variables as both inputs and outputs for making cross level ghosts. This is useful when working with modules that are saved separately and can be modified in that way. The is set from the Context Menu for a variable. There is also a new option added to the Model Settings Properties Panel that will suppress module connection errors.

Simplified Equation Error Fixing

Equations that are either missing inputs, or have extra inputs, can now be fixed by clicking on the error message in the Equation Tab. The related connectors will be added to, or removed from, the diagram. Learn More

Performance Improvements

Simulation speed has been increased for larger models and the long wait time that sometimes occurred as a simulation was beginning reduced. LTM has also been improved for large models requiring algorithmic search to detect loops.

Updated Data Manager

A Restore button has been added to the Data Manager dialog and loading parameters from a run now opens the Load Parameters dialog giving you more control over which equations are overwritten with values from the run.

More Export from Interface Options

The Export Parameter Values selection from Actions (Interface) for Button (Interface) now allows you to specify which parameters in addition to those that have been changed to export. This allows the creation of more complete import data sets. There is also an option to export only a single value.

There is also a new action to export the variables in a Table making it easier to keep exports up to date with your needs.

More Multiplayer Options

An option has been added to prevent multiplayer games to continue when a player drops. This is set in the Multiplayer Options dialog, which has also been improved for usability. Learn More

Improved Browser Control

There is now an option on the Publishing Options dialog to prevent the current page from displaying in the URL for a published Sim App. This prevents users from skipping pages and also makes your interface appear as a single page to the browser so that the browser's back button will leave the interface altogether rather than navigating within it. Learn More

December 6, 2021 - Stella 2.1.5

Vertical and Folio Navigation Control

The Navigation Control (Interface) now has the option to display vertically (tabs stacked one on top of another) or in folio orientation (text running up from the bottom). This provides more flexibility around the appearance of navigation choices on the interface. Learn more

Enhancements to Stella Live

It is now possible to change graphical functions in a model just as you can change constants in Stella Live. Simply open the Results Panel and click on the button on the bottom to open the Graphical Editor dialog box. The model will be simulated with the changes you have made (but no change will be made to the model equations).

The option to turn off Stella Live updates when moving knobs has also been added to the Model Settings Properties Panel. Turning this off is helpful for larger models that take significant time to simulate.

Import Improvements

When there are imported variables in a model the tooltip for the variable will name the active import source file (and sheet if appropriate). This makes it easier to determine where data is coming from.

Messages displayed when testing imports in the Import Data dialog box have also been improved to make it easier to find the source of errors. Learn more

Update When Stopped Option on Interface

There is now an option in the Numeric Display Properties to update on user input when stopped. This allows values to be updated after a run has finished and will display the currently computed value (effectively the beginning value for the next run) rather than the last value for the run just completed. Learn more

Resetting Controlled Values After an Interval

In addition to resetting after 1 time unit, you can now have a control (such as a slider) reset after any amount of time. This is specified in the options for the individuals controls such as the Slider (Interface). Note: If you work with a model using this feature in an earlier Stella version you will lose these settings. Learn more

Page Animations Option

There is now an option whether to create an animation when switching between pages on a published interface. For interfaces with consistent backgrounds on different pages the transition animation can be distracting and have been turned off by default. It can be changed on the Interface Settings Properties Panel. Learn more

New Builtin for Number of Sensi Runs

There is a new builtin that shows the total number of runs that will occur during sensitivity. The builtin is SENSIRUNTOTAL and is detailed in Miscellaneous builtins. This can be very useful for displaying progress on the interface. Learn more

Setting Arrays on Flows

It is now possible to set the arrays on inflows into non-arrayed stocks. This can be convenient when setting attributes for different array elements flowing into conveyors and queues. Outflows continue to inherit the array settings of the upstream stock unless they are connected to a downstream stock arrayed differently.

Font Size on Expanded Graph on Interface

When using the expand button on interface graphs smaller fonts will be enlarged to make the graphs easier to read. Learn more

Multiple Selection for Document Tab

You can now apply the document tab with multiple variables selected. If they share the same documentation or units (or if they are all empty) you can specify either for all of the selected variables by editing once. Learn more

Import Directly from isdb Files

From the Data Manager when you click on the button to load external data as a run, you can now directly use an isdb file from a different model, or a previous version of the model you are working with. This makes it easier to compare results across models without an extra export step. Learn more

September 14, 2021 - Stella 2.1.4

LTM Improvements

It is now possible to aggregate similar loops, and purge canceling loops. This makes it easier to find and visualize multiple loops that have similar effects and to make more compact explanations of behavior for complex models. See Loops That Matter™ Overview for more discussion and Loops Panel for details on setting options.

Graph Improvements

Bar graphs can now be displayed over time. See Bar Graph for more discussion.

The Dots only option on line graphs is now applied by series, making it possible to mix and match dots and connected lines. See Graph Series Property Panel for details.

Graph axis ticks can now be applied to increase readability. See Graph Settings Properties Panel

We have also streamlined the settings for histograms to make them more intuitive. See Graph Series Property Panel for details.

Import Template Improvements

For import templates created from the Create Import Template dialog box the default format for one dimensional arrays now includes the array name, and there are options to get element by element listings of arrays. It is also possible to add units of measure as a means of documentation. Learn more

July 15, 2021 - Stella 2.1.3

Native Mac ARM Support (PreRelease)

Stella now runs natively on the new Apple Silicon Macintosh computers. These new computers are fast, and running without Rosetta makes them faster still. Though we have not completed all testing (thus the PreRelease flag) so far we have not found any differences to the existing Mac products and you will see a big boost in performance if you have one of the new Macs.

Simplified CLDs for specific loops

In addition to being able to highlight loops on the stock and flow diagram, it is now possible to create a simplified CLD for a loop, or loops, of interest. This is an excellent way to highlight structure generating behavior and provide compact and uncluttered views of it. Learn more

Chat logs added to data collection

It is now possible to record chat logs in multipliayer games with data collection enabled. See Publishing Options dialog and Chat Log for more detail.

More control over queues and non-negative stocks

It is now possible to mark specific queues and non-negative stocks as not-passthru rather than having the software do this automatically. The algorithm for determining which stocks will constrain outflows without considering inflows has also been improved to work more consistently with macros and arrayed variables. Learn more

Accumulated option for discrete graphicals

When creating discrete graphicals there is now an option to treat them as accumulations so that they will render as a continuous output with the same total area under the curve. This is useful, for example, in breaking up annual demand into value changing slowly from month to month. Learn more

Loops that Matter output for Stella Simulator

The results of the LTM computation can now be saved from Stella Simulator, allowing continued analysis of models. Learn more

June 1, 2021 - Stella 2.1.2

Stacked Bar Graphs

There is now an option in bar graphs to stack them. This allows you to create comparative graphs of more than one variable and display them at selected times. Learn more

Area Graph Improvements

Stacked graphs have options to display either summed or individual values and also to show values only in the legend on scrub. Learn more

Span Sliders on the Interface

A Span Slider has been added that allows a range to be set for two variable that represent a lower and upper (or min and max) value of the same concept. This is very useful for controlling sensitivity ranges. Learn more

Arrayed Placeholders

You can now array placeholders. This allows them to be used in graphs with a * and wildcards so that a single graph can be used to show large number of different combinations of values. Learn more

Subrange and Parent-Range Improvements

In additions to using a subrange for a variable arrayed by the parent range, it is now possible to use the parent range in a variable arrayed by the subrange. This makes it much easier to move back and forth between partial and full range equations. Learn more


The PERCENTILE builtin allows you to look at the distribution of values within an array slice - making a generalization of the MIN and MAX builtins when used on arrays and also allowing the computation of a median and any other percentile. See Array builtins for details. The LOOKUPRANDOM builtin allows you to specify an arbitrary PDF and then pull values from that. See Statistical builtins for details.

Array Improvements

Changing the array dimensions for a variable will now change many of the equations it is used in to reflect the updated dimensions. This should decrease tedious hand work. Importing arrays is also not more flexible allowing blank cells to be used in the import definitions making it easier to set up subranges. Learn more

Preparing Import Sheets

A convenience feature has been added to the Arrayed Equation editing dialog that makes it easier to set up import sheets one variable at a time. Learn more

Graph Duplication

A feature has been added to duplicate the current graph in a pad. This simplifies creating a number of quite similar graphs. Learn more

Adding Units to Constant Lists

The Create Import Template dialog box now has an option for add units to the variables listed. This can be helpful when using constant lists as part of a documentation process. Learn more

March 5, 2021 - Stella 2.1.1

History Across Runs

The HISTORY builtin can now be used to get values from different runs. This makes it easy to make use of values in a base run, and also to perform operations across runs. Learn more

ISNAN Builtin

The ISNAN builtin checks to see if a variable has the value NAN. This is useful with the HISTORY builtin and also when working with data. Learn more

Duplicating Array Dimensions and Subrange Improvements

There is now a convenient way to duplicate an array dimension using the Array Editor dialog box. This can be helpful when working with Subranges. Subranges will also now be displayed when selecting variables into equations. Spell checking has also been added to the Array Editor.

Improved LTM Highlighting

Feedback loops that go through flows, but not their connected stocks, are now visually distinct from those that go through both the flow and the stock.

Improved CLD Diagram Generation

It is now possible to adjust the symbol and name size on causal loop diagrams generated using LTM making them much easier to read. Learn more

January 15, 2021 - Stella 2.1

Sensitivity on the Interface

Sensitivity simulations are now supported on the interface. To start a sensitivity select Run Sensitivity for the button action as described in Actions (Interface). The sensitivity run will execute and graphs and tables will update as runs are completed.

Percentile Graphs and Histogram on Interface

You can now place percentile charts (across runs) and histograms (across runs or time) on the interface. These work the same way that they do on the model and will repopulate as sensitivity runs occur. See Bar Graph for more details on histograms and Graph Series Property Panel for more details on confidence graphs.

Parametrized Sensitivity Values

In addition to specifying bounds for sensitivities as numbers, you can also specify model variables to use for the bounds. This is most helpful when performing sensitivity on the interface as it allows the interface to specify the range over which to perform the sensitivity. This range can be directly under user control, or specified in the background based on other user selections. Learn more

Improved LTM Computations

We have improved the link score computations for the effects of flows on stocks by using the change in flows relative to the change in net flows rather than the flows directly. The new computation gives results that are largely independent of the exact flow formulations used and generally improve continuity of the loop dominance measures. Learn more

Controllable Start and Stop Time

In addition to specifying numbers for the time at which a model starts and stop you can also specify model variables. This is done in the Model Settings Properties Panel by selecting a model variable for the associated time. You can use any model variable, computed or controlled. If there is an issue determining the proper start time and error message will be displayed.

Multiple Selection in the Find

You can now select multiple variables in the find, including selecting variables in different modules. This makes it possible to change the array settings on multiple variables at once and also to add multiple variables to tables, graphs, and summing converters. Multiple selection is done using Shift or Ctrl + Click as described in Find Window.

Direct Dropping of Variables onto Summing Converters and Placeholders

You can now drop variables directly into summing converters and placeholders, either by selecting them on the model or in the Find Window. Learn more

Better Control over Dimension Changes

The Array Tab of the properties panel is now available when there are multiple variables selected - whether on the diagram or in the Find Window. This makes it possible to set, or add to, the dimensions for multiple variables.

Cleaning Time for Ovens

Ovens now have a cleaning time that keeps them idle after the completion of processing. This makes it easier to represent turnover where there is a required set up or recovery time before the next item can be processed. Learn more

Excluding Legends from Graphs

Graph legends can be selectively excluded to reduce clutter and make more area available for drawing the graph. Learn more

Improved Opening of Vensim® Models

The opening of Vensim models is smoother with unrecognized functions brought directly across and better array support. Learn more

November 25, 2020 - Stella 2.0.3

Added Load Run Option to Stella Simulator

It is now possible to load in data as a run in Stella Simulator. This is most useful for calibration runs. Learn more

Updated SIZE Builtin to Allow Dimension Names Directly

When using the builtin SIZE to provide the number of elements in an array dimension you can now simply specify the dimension name. Learn more

Improvements to the Opening of Vensim Models

The translation utility has been updated to handle more Vensim models, especially those that use flows as inflows to (or outflows from) than one stock equation. Learn more

November 16, 2020 - Stella 2.0.2

Initialization Options for Conveyors, Queues, Ovens and Cycle Time Stocks

It is now possible to use equations to specify the internal content of conveyors and queues, as well as to specify the initial values of attributes and cycle time within stocks. These additions allow a model to be initialized in a way that is representative of the true initial state of the system (for example a conveyor with initial growth). Learn more

Optional Equation Conventions

To simplify setting optional equations rather than having to turn on and off specific optional equations, such as that to arrest a conveyor, the equations can now simply be left blank. Learn more

Streamlined Find

The interface used to find variables has been streamlined to make it easier to perform the most common tasks. Learn more

Causes and Uses Display

The right click menu can now be used to show the causes and uses of a variable. In addition, the causes and uses now list both first and second order causes and uses, making it easier to visual dependencies. See Context Menu and Causes Uses for discussion.

Automatic Timer-Based Game Advancing

You can set up multiplayer games to automatically advance based on a timer. This forces games to continue even when some players have not met the deadline of committing their decisions. Learn more

Invariant File Content

Files saved will no longer change when there have been no changes to the underlying model because of the sequence in which content is written out, or dependencies on internal object IDs. This includes modules saved as separate files which facilitates use with version control systems. Learn more

Improved Report as Options for Interface

The "Report as" option associated with a converter will now be used on the interface to determine whether the current value of the variable will display when a model is paused. Selecting stock will ensure that the current value is always displayed (even if it might change after resuming). Learn more

Outline-only Diagrams on the Interface

An option has been added to allow diagrams to draw only the outline of shapes. This is useful when you are using a diagram to overlay other content. Learn more

Duplicate Connectors Give Option to Replace Old Connector

If you draw a connector that already exists you will have the option to replace the old connector with the new. This is helpful for moving connections to ghosts, and also rearranging connectors in busy models.

New Keyboard Shortcuts

You can now use Ctrl+E to switch to edit Model and Shift+Ctrl+E to switch to explore or experiment mode. A full list of keyboard shortcuts is available at Keyboard Shortcuts and Key Combinations.

September 14, 2020 - Stella 2.0.1

Allocation Based on Targets and Preferences

The new builtin ALLOCATE allows allocation of quantities taking into account both availability and attractiveness. This can be used to allocate a supply to different consumers, or to allocate demand to different producers. Learn more

Support Precision on Graphical Inputs

You can now specify a precision for graphical inputs on the interface allowing, for example, to keep to integer values. Learn more

Find All Uses of a Dimension

It is now easy to find every variable that uses a given dimension. This is useful for when dimensions are changed, and also for finding unused dimensions. Learn more

Loop Highlighting Across Modules

Loops that cross modules will now highlight the modules involved in the loops and the associated module connectors (if they represent only a single cross level connection). This makes is somewhat easier to follow loops across modules, but the automated CLD view may be a more effective way of visualizing such loops. Learn more

HTML Tags in Text Boxes and Annotations

You can include html tags in text boxes and annotation on the interface. These will display and behave the way they would in a web page, and can provide a convenient way to add links (or embed content) in interfaces. See Text Boxes and Annotation Button (Interface).

June 10, 2020 - Stella 2.0

Loops That Matter

Understanding models has never been easier! Loops that Matter is new functionality in Stella 2 that allows you to immediately visualize the impact of every variable in a model on every other variable during the course of the simulation. The software identifies the feedback loops important to generating behavior and allows you to create causal loop diagrams that display those loops in a simplified form. Learn more

Automatic Diagram Layout

Stella will now create stock and flow diagrams, or fill in missing pieces, for models created in other applications and brought in to Stella. Learn more

Model Equation in Table

The Equation Viewer will now display equations in a table, making it much easier to read and navigate through the listing. The table can be saved to html or copied to the clipboard in for pasting into a spreadsheet. Learn more

Highlighting Non-negativity Constraints

When a flow is forced to 0 because of a non-negative stock, both the flow and the stock will now highlight to show that this has happened. Hovering over the highlighted stock or flow will give a message showing what type of constraint was encountered. There is an option in the Preferences Dialog to allow disabling of this feature and an option in the Model Settings Properties Panel to turn it off for a specific model.

New Builtins

The LOOKUPMEAN builtin can be used to compute the mean value of a graphical. This is most useful for graphicals on the range of 0 to 1 representing probability density functions. The builtin MLPANN can be used to embed artificial neural nets in models to capture arbitrary nonlinear relationships. Learn more

Distribution profile for Conveyors

Material coming into a conveyor is normally put at the beginning, then sent across the conveyor over the course of the simulation. It is now possible to distribute the material over the conveyor following the contour in a graphical. This effectively allows arbitrary residence time distributions which provides more accurate modeling in cases where the time in stock is variable. Learn more

Stella Live on the Interface

We have added the ability to create an interface where Stella Live is always on. Simply set this option in the Interface Settings Properties Panel. There is also a new action to first run a model, and then enter Stella Live, mimicking the behavior of the run button during model development (see Actions (Interface)).

Save to Disk option on Optimization Log

You can now save an optimization log to disk during the optimization. This allows recovery in case of a software failure which is valuable for optimizations that run for long periods of time. Learn more

Data Collection from Stella Live

During data collections the results from the last Stella Live run can now be captured. Learn more

February 27, 2020 - Stella 1.9.5


It is now possible to create and use subranges to simplify both array operations and the selection of values from arrays with different dimensions. See Subranges for details.

CLD Page Size

You can now set the size of CLD pages making it easier to organize your content. See CLD Style Properties Panel for details.

November 18, 2019 - Stella 1.9.4

Export Data Options

We have added an option to include precomputed converters and flows when exporting data. Learn more

October 16, 2019 - Stella 1.9.3

Runs Comparison

We have added a function that allows you to quickly compare two runs. This makes it easy to track down differences between runs, especially differences resulting from changes in constant or graphical values. The Runs Comparison window reports the differences between two runs and the first time those differences occur. It is opened from the Open Runs Comparison command on the Windows menu. See Runs Comparison for more details.

Simulation Duration Control

You can now control the speed at which a simulation progresses using a variable(rather than the old simulation speed control). Simply select the model variable you want to define the simulation duration with in the Model Settings Properties Panel. You can use a slider or other input device the then set the simulation duration or speed. You can also vary the simulation speed based on model conditions.

Save List Based Export Definitions

There is an additional export option that reads a list of variables from a file and then exports values for those variables. This is most useful for batch processing where the list of values to view is not known ahead of time and can be written to a file allowing a model to report different results without having to edit the model. See Export Data dialog box for details.

Improved Unit Definition Facility

It is now possible to create definitions for units that already have built in definitions, effectively replacing them. This makes it easier to have units suited to your needs. See Unit Editor dialog box for details. This dialog has also been improved so that double clicking is not required to edit unit definitions. In addition, changes to unit definitions are now tracked in the undo/redo system. We have also added Tons and Tonnes to the built in definitions.

Causes, Uses, and Selection History

The selection history panel has been replaced with menu items in the Equation Tab of the Properties Panel and also on the Results Panel. These menu items allow you to look at the previous 10 variables you have worked with and, if you select a previous variables, the next ones that you worked with.

More Control over Decimal Character

You can now override the settings for your computer to choose whether a , or . should be used as the decimal delimiter. This is done from the Preferences Dialog.

More control over paging when dragging model elements

When dragging things on the model dragging off the current boundary of the model will no longer aromatically add pages. Instead the page will be added only after you release the mouse button. Thus, moving off then back onto the current model extent will not cause a change in the number of pages used for the model diagram.

Border Radius on Text Box and Annotation Popup

You can now set the border radius on text boxes (Text Box Properties Panel) and annotation popups (Annotation Button (Interface)).

Zero Line on Graphs

There is now an option to add a grid line at 0 on graphs. See Graph Settings Properties Panel.

August 23, 2019 - Stella 1.9.2

Attribute based Queue Dispatch

Queue outflows can assign a list of attribute values that they will dispatch. This allows downstream routing of material flows based on attributes without having to create separate flow channels for common processing resources. See Queue Computation and Equation Tab for more discussion.

Element by Element Equation Dependencies

You can now use expressions such as SELF[Dimension-1] inside of equations to reference prior (or later) elements in arrays. See SELF for an example. Similarly, you can create loops with apparent circularity that resolve on an element by element basis. See Referencing other Array Elements for more discussion.

Setting Converters to Display as Stocks

We have generalized flow concept to allow you to specify that a converter should be reported the same way a stock is on tables. This is most useful on the interface, where stock values are reported at the current time when a model is paused, but converter values are not. It is also helpful on financial tables, where converter values are reported one DT in advance of the reported time for stocks (the end of period concept). See Scales and Ranges Tab and Financial Tables for details on setting these.

Number Formatting on Tables

There is now a number formatting button on the panel used to set up tables and financial tables, making it easier to adjust these to your needs. See Table Properties and Financial Tables for usage.

Simulation Log Improvements

The simulation log only opens when model opens if there are errors to report. Parameter overrides are still reported, but will not cause the log to open. There is also a new shortcut on the Run Toolbar to open the Simulation Log whenever it has content.

June 19, 2019 - Stella 1.9.1

Internal Rate of Return

There is a new builtin IRR that computes the internal rate of return on a stream of payments. Learn more

Attribute Specific Cycle Time Metrics

The Cycle-time builtins now take an optional attribute range which allows you to look at the characteristics of batches with specific attributes. Learn more

Filtering for Dynamic Causes in Causal Lens

The causal lens allows you to (and by default does) filter out causes from initialization as well as constants when looking at the causes. This removes variables that do not directly contribute to the dynamic behavior of another variable. Learn more

May 21, 2019 - Stella 1.9

FIFO Conveyors

There is now a FIFO option on conveyors so that they maintain material in the order received and respond immediately to changes in transit time. See FIFO Conveyor Computation for more discussion. Conveyors are marked FIFO in the Conveyor parameters.

Discrete Attribute Tracking

You can now set an attribute on flows that are connected to discrete stocks (and non-negative stocks in Cycle-Time Mode). The attributes can be measured on downstream stocks and flows and can optionally be used to prioritize material for processing in queues. See Attribute and Cycle Time Tracking for an overview, Flow options for a description of how to set the attribute, and Discrete builtins for the new builtins used to measure the attributes.

Prioritization of Material Entering Queues

The discrete attribute can be used to prioritize material entering the queue (so the queue is not longer FIFO). This allows material from different sources to be processed differently. See Queue parameters for the use of the attributes to prioritize material flowing into queues and Queue Computation for more discussion of how the material is ordered.

Round Robin and Prioritized Queue Dispatching

Queue dispatching to multiple places now allows you to set priorities for destinations and will provide a round robin mechanism to make use of all available destinations (typically ovens). See Queue parameters to set the parameters and Queue Computation for more discussion of how the priorities are used.

Queue Purging

Material that has been in a queue for too long can now be purged from the queue through an outflow that is only active when the age of material has exceeded a threshold. See Flow options to set a flow so that it will purge a queue and Queue Computation for more discussion of the way purging works.

Spreading of Conveyor Inflows

Conveyor inflows can now be marked to be spread across the existing material in a conveyor rather than added at the beginning of a conveyor. This is useful when parallel conveyors are tracking similar groups of things, such as aging people, and one conveyor leakage can be used to introduce material to another as it would with incidence of a disease. It is also useful in demographic modeling in general as it makes is much easier to deal with immigration and emigration. See Flow options to set the flow and Spreading Conveyor Inputs for more detail on how this works.

Graphical Presets

Graphical functions now have a number of suggested forms available that make it easier to draw smooth curves. Learn more

Inverse Graphical and Graphical Area Builtins

Two new builtins have been added to make it easier to work with graphical functions. LOOKUPINV will invert a graphical so that, if the graphical is monotonic, the value of the input required to get the specified output will be returned. LOOKUPAREA will return the area underneath the graphical up until the indicated input value. Learn more

ROOTN Builtin

The ROOTN builtin returns the nth root of the first argument. Learn more

Importing Array Definitions

You can now define the elements of an array (both their names and the number of them) using Import Sheets. This allows you to change the specific content of array elements without having to edit the model, and can be very useful for data intensive model set up. Learn more

Pyramid Graphs

We have added a new graph form that allows you to represent two sets of equally sized array entries on the left and right hand side of mirrored horizontal bar graphs. A common use of this is a population pyramid which shows the number of people by age group separated by sex. Learn more

Horizontal Bar Graphs

The bar graph now has a variation in which the bars are drawn horizontally instead of vertically. With the exception of orientation, the options and behavior of the two types of bar graphs is identical. Learn more

Financial Tables (Interface)

A new financial reporting style table has been added on the interface to make it easier to present information in the style of financial reports. It allows formatting, including font and color, to be applied line by line. Learn more

Expandable Graphs on the Interface

When you place graphs on the interface you now have an option to provide an expansion button for the graph. This will make the graph bigger, and also provide a control so that the interface user can zoom in to see a narrower time range on the graph. Learn more

Published Accessibility Options

Published interfaces can now support keyboard input and alternative text to improve accessibility. Learn more

Arrays in Graphs

You can now add an entire array (or a slice of an array) to a graph and have it stay in the graph in that form. This simplifies graph definitions and improves labeling while also supporting changes to array element definitions without having to rebuild a graph. Learn more

Usability Improvements

We have made a variety of usability improvements that should make it easier to build and use models including:

  • The addition of variables to graph and tables is now more intuitively done using the green plus button to add all variables, including the first.
  • The annotation object on the interface no longer displays its invisible button. Some icons and text have been updated to clarify meaning.
  • The zooming feature on the Results panel and Causal Lens have been improved and synced.
  • The causes and uses button that lets you navigate has been made to look more like a button.
  • Placeholder text and labels have been improved for clarity.
  • Panel layout and tab ordering has been cleaned up.
  • Selecting interface objects from the toolbar that need special model structure to work give better messages.
New Slider Style

There is a new style of the slider (horizontal only) that can give your interface a more modern look. Learn more

Spell Check Panel

There is now a panel that will open and list all spelling errors that have been found in variable names. Improvements have also been made to the ignore selection in spell check so that anything ignored will be remembered with the model. Learn more

Module Navigation Panel

The module navigation panel allows you to see all the modules in a model and their containment structure in one place. It is a very useful device for quickly navigating through large models. Learn more

Module Labeling

You can now put labels on modules so that the module name used in graph, tables, and cross level references can be short, while the name displayed on the module can be more descriptive. Learn more

Model Bundling with Supporting Files

The file menu now has a function to export your model as a bundle. This creates a zip file including your model and all supporting files (images, movies, import sources and export destinations). Learn more

Lead-in Time Improvements

If you specify a lead-in time for use in an interface then results will always be shown till the lead in time in presentation mode and when published (no blank graphs). Learn more

Lock Diagram

A new option to lock a model diagram can be used to prevent any movement of variables or other objects in the model. This is useful for preventing inadvertent changes or reminding others that things should not be changed. Learn more

March 12, 2019 - Stella 1.8.3

iframe Embedder

Allows you to imbed an iframe into an interface page supporting surveys and inclusion of content from other websites on the interface. See iframe(interface) for more information.

Units Check Improvements

The messages related to units issues for unit converting flows have been improved. Checking has also been added for conveyor transit times, conveyor capacity limits, conveyor inflow limits, and oven cook times.

Background Color on Text Boxes

Selecting a text color close to white no longer requires that you set the background in the editing window to see the text. Instead the lack of contrast is detected and a different background used automatically. See Text Box Properties Panel for more about Text Boxes.

Improvements to Legends on Scatter and Bubble Charts

The legends now use a square instead of a line segment to show what is being displayed. See Scatter Graph and Bubble Chart for details on these two graph types.

January 10, 2019 - Stella 1.8.2

Stella Live with Arrayed Variables

You can now see results for arrayed variables and adjust inputs via knobs when using Stella live. The array elements being displayed or changed are determined by the selection you make in the Results Panel. When you open a model the first elements of each array will be selected.

Array Wildcards

By using array wildcards you can set up graphs, tables, and other output and input objects to display different elements of an array based on user selections. On the model layer this works very much like Stella Live with arrayed variables, on the interface it provides flexibility in page design and can also be used to simplify multiplayer game design as described in Using Wildcards for Multiplayer Games. For more information see Wildcards.

Placeholder Variables

Place holder variables allow you to create graphs, tables, and other input and output objects that can be used with different variables based on selections you or an interface user makes. This makes it possible to reuse parts of an interface page, or an entire page, to represent different parts of a model. It also allows the creation of graphs, tables, and numeric displays on models that can be switched by changing which placeholder variable is selected via the Results Panel. For more information see Placeholders.

Confidence Bounds

Confidence bounds allow you to see how much an optimization parameter can change in order to have a specific influence on the resulting payoff. Most commonly they are used to bound parameter estimates resulting from a calibration, but they can also be used in outcome optimizations. For more information see Calibration.

Optimizer Log

We have improved the reporting of information from optimization by writing it to the Optimizer Log which allows you to see more clearly the results, and also to look back at previous optimization runs in an organized manner.

Export Changes from the Interface

We have added the ability to export the set of variables that have been changed on the interface, both constant values and graphicals. This makes it possible to save the settings for a run made on the interface and then reload them at a later time. See Actions (Interface) for details.

Performance Improvements

We have improved simulation speed and model save time for large models with complex equations.

November 21, 2018 - Stella 1.8.1

Team and Player Assignments in MultiPlayer Games

Team and player assignments allow you to set up classrooms with individuals assigned to specific teams for a multiplayer game. Learn More


This new builtin allows tracking of the run number within a sensitivity run. This is useful if you want to set something specific, such as a noise seed, based on which sensitivity run is occurring. Learn More

Allow use of SELF in ENDVAL

The SELF builtin can now be used in the ENDVAL builtin, allowing customized definitions of RUNCOUNT. Learn More

Display Time Bounds for Scatter and Bubble

The Scatter Plot and Bubble Chart now allow you to specify the time range from which values should be drawn. Learn More

October 26, 2018 - Stella 1.8


Calibration is the process of adjusting model parameters to make the behavior line up with a target, most commonly measured time series data. It is now easy to set up payoffs and use the optimization engine in Stella to accomplish this. Learn More

Importing Time Varying Values

Time varying values allow you to have variables take on different values at different times based on the imported data. This is useful as a mechanism for bringing in a sequence of decisions or controlling values, and also loading in data to be used in calibration. See Import Data dialog box for more details and Defining Calibration Payoffs for the use of imported time varying data in payoff definitions.

Optimization from the Command Line and in Stella Simulator

The -ro option has been added to the command line to run optimizations. See Running Models Using the Command Line for details.

The same option has also been added to Stella Simulator, as has support for sensitivity and more control over initialization. See Stella Simulator Arguments for more details.

Printing of Interface Pages

Print and Print Preview have been added to the File menu on the interface window. These will print the pages currently displayed in the Page Preview Panel. Learn More

Sobol Sequences for Sensitivity

There is an additional option to use Sobol sequences when preforming multivariate sensitivity. Sobol sequences are designed to maximize the exploration of multidimensional parameter spaces. Learn More

Replacing Runs

It is now possible to replace a run with another run so that any graphs or tables referring to the run will be updated. For example if you have a run named base, you can have the current run replace it. Learn More

Units in User Macros

You can now specify the units of measure for a User Macro based on the units of measure of the arguments to the macro allowing full checking of model units. Learn More


There is a new function INTERPOLATE that will take an N dimensional set of points and return the value derived by interpolating between these point values. In one dimension this will act the same way that a graphical would on a vector of numbers. In higher dimensions the interpolation is between planes (or hyperplanes) of the different dimensions. Learn More

Lead-In Time and Restore Inputs Options (Interface)

You can now set runs to start part way into the simulation when working on the interface. This is convenient if you want users to start with some results already available. There is also an option to restore inputs when starting new runs, which is very useful for multiplayer gaming. Learn More

Shape Tool (Interface)

The shape tool makes it easy to add vertical and horizontal separators on interface pages as well as to include outlined or shaded ellipses (including circles) and rectangles. Learn More

Hover Tips in Graphical Inputs (Interface)

There is now an option on Graphical Inputs to display the current x and y values as the user drags the points in the shape. This is especially useful for discrete graphicals. Learn More

Hover Tips on Sliders (Interface)

You can now control when hover tips appear on sliders (always, never, or when the user is dragging the slider). Learn More

Numeric Display Number Formatting

You can now specify number format for the numeric display in the properties panel. This allows you select multiple numeric displays and set the formatting options for all of them together. Learn More

Loop Indicator on the Interface

If you include Loop Indicators on your model they will now be active when the model structure is presented in either a model view or on a story in the interface. Learn More

Simplified Inclusion of CLDs

Causal loop diagrams created in the new CLD Window will now have NAN equations automatically added. These will simplify the inclusion of CLDs in simulating models as they will no longer create invalid equations. The NAN(a,b) format can be added by hand when working in regular models (see Creating CLDs).

Added Mojave Support on Macintosh

Stella will now work with the features in the newly released Mojave operating system on the Macintosh including the dark mode interface selection.

Importing to a Module Maintains Cross Level Ghosts

When you replace the contents of a module using the Import button any cross level connections between the module and the rest of the model will be retained as long as the names in the model for inputs and outputs have not changed. See Module Properties Tab for more discussion or Agent Based Examples for a typical usage.

August 27, 2018 - Stella 1.7.1

Simplified Causal Loop Diagram Creation

You can now ask for a new causal loop diagram and have the simplified toolset necessary for creating causal loop diagrams. That toolset makes the creation and editing of CLDs quick and easy. It also matches the toolset of the Online CLD Editor. Learn More

Switch Color

You can now set the color that a switch on the interface displays when it is on. Learn More

Graphical Input Appearance (Interface)

You can now set the line color for the graphical input on the interface and also specify a fill intensity to display color below the line. Learn More

Integer Option on Allocation Input (Interface)

The Allocation Input object now has the option to computer only integer values allowing more control of both the values and the label appearance. Learn More

Offline Help Files

There is now a menu option to download the help files as a zipped archive for use offline. This allows you to view the help files locally when you do not have an internet connection. Learn More

Sharing Models and CLDs Online

We have added to the options for sharing Models and CLDs online allowing you to give other people access to your work without marking it as creative commons. This option is not available in the free online editor. Learn More

Causal Lens Improvement

If there are long variable names in the causal lens, you can now Hover over to see the full expanded name. Learn More

Multiple Leakage Control

When a conveyor has multiple leakages with different leak zones you can now specify whether the leakage fraction on later leak zones applies to the inflowing quantity or the quantity that has remaining after the earlier leakages. Learn More

July 30, 2018 - Stella 1.7

Navigation Control

The Interface has a new tool used to add a set of navigation links to an interface page or template. The bar of navigation links can appear as a row of tabs or buttons. The styling includes radius corners and spacing. Learn More

Spell Check

You can now spell check for variable names, documentation, and labels. You can select different dictionaries in the Preferences Dialog and correct misspellings using the Context Menu.

Encapsulating Sectors and Selections into Modules

There is new functionality to take a selection of variables, or a sector, and create a module with the appropriate cross level connections into and out of it. This makes it easy to simplify models that have too much detail built up in any given module. Learn More

User Defined Macros

You can now create reusable pieces of model structure that can be used the same way that the builtin functions are. This allows you to create customized versions of commonly occurring patterns such as cascaded delays as well as more specialized functions. Learn More

Bubble Charts

Bubble charts allow you to display three different dimensions of attributes on a single graph. These graphs represent a snapshot of values at a time and will animate during simulation or when dragging the time slider. Learn More

Mixing Graphs and Tables in Containers

You can now create a container that includes both graphs and tables making it easier to provide the output you want without using up real estate. See Graph Series Property Panel and Table Properties for more details.

Run by Modules Improvements

It is now possible to turn modules on and off in Stella Live, while paused. Learn More

Conveyor Leakage Changes

Leakage computations on conveyors with a variable transit time have been improved to more accurately reflect the leak fraction or rate. Learn More

Interface Scaling Improvements

You can now set interfaces to scale prepositionally when they are deployed. This makes it easier to have interfaces that work on different devices without having to limit the minimum or maximum size (another added scaling capability). See Resizable Interfaces and the Resizable Options dialog for more information. Learn More

Multiple Entry Scatter Charts

Scatter charts can now have more than a single entry. This allows for comparison of x and y values across different runs or comparison of different sets of x and y values. Learn More

Irregular Time Axis on Imported Data

It is now possible to import data with arbitrary time values rather than requiring a uniformly increasing time axis. This makes it easier to accommodate missing values as well as values from different data sources. Learn More

Stashable Graphs and Tables

Stashable graphs and tables allow you to hold on to run results that are of special interest, while displaying the current run at all times. This is a convenient way to collect a sequence of interesting outcomes, and replaces the old functionality related to persevering and releasing data. Learn More

Picture in Picture Module Viewing

It is now possible to peek into modules without navigating into them. This allows you to see what is happening in a module while still looking at what is happening on the parent model of that module. This allows you to make changes in Stella Live and see the consequences of those changes in another module. It also allows you to get an overview of module structure without losing your current visual focus. Learn More

Model Compare

A new feature has been added that allows you to compare the model you currently have open with another saved model. This is a convenient way to see what changed have been made for models derived from one another or a common source. Learn More

Narrowing Time Range for Results Panel and Causal Lens

You can now zoom in on the displayed time in the Results Panel and Causal Lens. This makes it easier to trace down sources of behavior at a point in time, as well as seeing changes in behavior between multiple runs. See Results Panel and Causal Lens™ for details.

Vertical Sliders

There is now an option to display sliders vertically as well as horizontally. Learn More

Collapsable Panels

Many of the panels now include sections that can be collapsed if you do not needs to refer to it. This decreases the amount of information displayed on the panel and thus easier to work with. Learn More

Equation View Enhancements

We have added options to the equation viewer to make it easier to provide written model documentation to meet the requirements of peer reviewed journals such as the System Dynamics Review. Learn More

Line Graph Updates

You can now specify that graph be drawn without connecting the points into line. Learn More

Button Highlighting on Mouse-Over (Interface)

There is a new option to have buttons change their appear as the mouse cursor passes over them. Learn More

Aligning Objects

When you select 3 or more objects on the interface there is now a menu option to either align or distribute those objects to clean up layout. You can keep the movement of objects completely horizontal or completely vertical by holding down the Shift key. This works on both the model and the interface. Learn More

Loop Indicator Improvements

The loop indicator now works by selecting all of the elements you want highlighted. This allows you to select more specific loops or parts of structure for display. Learn More

Find Persistence

The find will now retain what you are searching (Variable Name, Equation or Documentation), the order in which to display results, and whether to search in the whole model, the current module or the current module and modules it contains.

Sensitivity Improvements

You can now provide an external list of parameters to change when running sensitivity analysis, and we have changed the sampling for Ad-Hoc and Incremental when running a limited number of runs to better support random selection of discrete values. Learn More

Improved Security Settings

We have made a number of internal improvements to the security settings and fixed issues that arose from specific character combinations in low security passwords. One consequence of this is that models saved in the current version using security settings will not open in versions before version 1.7. Learn More

Improved Opening Time

Large models should now open more quickly.

April 16, 2018 - Stella 1.6.2

Optimization within Sensitivity

In addition to being able to run optimizations over sensitivity runs you can now run an optimization within each sensitivity run. This is a convenient way to see how the optimal parameters found vary based on other model parameters or noise seeds. Learn More

Constraint Handling in Differential Evolution

It is now possible to add constraints to differential evolution optimizations allowing the specification of inadmissible search spaces without degrading the efficiency of the search. Learn More

Find Options

The find tool now makes it easier to look for content that appears in equations and documentation by allowing you to specify search terms within these. Learn More

Managing Time Formats

A Manage option was added to the right click (Ctrl-click/⌘-click) menu item for formatting items in graphs and tables. This will open the Manage Time Labels dialog box allowing you to add and modify formats as well as changing the default time format. Learn More

Table Position in Results Panel

The scroll position on the table in the Results Panel is now retained when moving between variables.

Documenting Models in the Equation Viewer

Options have been added to the Equation Viewer to make it easier to create model documentation that meets your needs. It will now display optional variable usage and provides increased control over annotation. Learn More

Sketchables with Fill

You can now fill in the area underneath a sketchable graph. This is especially useful when using area graphs.

Getting Outputs in the Sensitivity Parameters List

There is now an option to see both the inputs to each sensitivity run as well as the outputs in the currently displayed graph or table. Learn More

March 16, 2018 - Stella 1.6.1

Ghost Tool

If you click on an empty part of the model when using the ghost tool the Find dialog will come up allowing you to ghost a variable without first navigating to it.

Restore Window Layout

Under the Window menu on the model and the interface, the Restore Window Layout option will reset all window, panel and tool bar positions to where they were when Stella was first installed (isee systems default settings). Learn More

Zoom to Fit

In the Zoom control, a new option has been added to automatically adjust the zoom level of the model diagram or interface page so that all objects will be visible within the viewable space without needing to scroll. Learn More

View Results and Causal Lens

A combined View Results and Causal Lens has been added to the Online Model Editor. Learn More

February 15, 2018 - Stella 1.6

Global Number Formatting

You can now specify a model level default number format that will be applied to all variables instead of having to do this variable by variable. This is done in the Model Settings Properties Panel. The options are the same as they are for each variable, and variables can still be set individually as well. Learn More

Currency, Prefixes and Suffixes for Formatted Numbers

Instead of limiting output formatting to use a $ or % you can now specify arbitrary prefixes and suffixes for output numbers. Learn More

Time Formatting and Labeling

You can now format time to display years, months and days and not simply decimal values. Learn More

Variables Used in Graphs, Tables and Interface Objects

You can now find what graphs or tables (or interface object) a variable is used in by right clicking and selecting Find Uses on the right (Ctrl) click menu. See Context Menu for more details. You can also locate exported tables from the Export Data dialog box.

Published Model Performance

The performance of published models, especially simulation speed, has been dramatically improved and will, with a modern browser, match the performance on the desktop.

Importing and Exporting Data

It is now possible to import and export data from the interface for published models. These are both set up using a Button (Interface). When the button is clicked the user will be prompted for a file to upload or save to. Only .csv files are supported on the interface. See also notes in Creating Import and Export Files.

Simulation Speed Control

The new Simulation Speed control allows you to let the interface user set the speed at which the model simulates. Learn More

Object Visibility

You can now have objects be made conditionally visible based on variable values, or the role in a multiplayer game. This allows customization of the user experience based on the state of a simulation. Learn More

Display Time

Much like the progress bar in the development environment the Display Time object shows progress during a simulation and allows the user to scrub over different times in the simulation. Learn More

Support for Sound

You can now add a button that will play a sound, and have a sound be played in response to a simulation event. This works the same on the desktop and for published models, though supported sound formats vary by browser. See Button (Interface) and Simulation Event Action dialog for more detail.

Documentation on the Interface

You can now display equations, units of measure, and any documentation provided for a variable in a Model View. This material is displayed as the mouse moves over the elements of the model. Learn More

Negative Binomial Distribution

The NEGBINOMIAL (negative binomial) builtin has been added. This returns the number of failures that occurred getting to a specific number of successes for a given probability of success. Learn More

Truncating and Sampling Distributions

You can also specify a minimum, maximum and sampling interval so that it is easy to create truncated or sample distributions in models, and truncated distributions for sensitivity. Learn More

Quoting of Array Dimensions and Elements

You can quote an array dimension name and element names by putting double quote around them (as in "1-2"). This capability is in place primarily to support the importation of models translated from other languages. If you do create labels with quotes the model will not work in previous versions of Stella.

Probability Density Options on Histograms

The Histogram has had options added to appear as a probability density function (pdf) and cumulative density function (cdf). Learn More

Improved Variable Highlighting

Highlighting of variables is now easier to find even in dense models with lots of color.

Passing Parameter Information for Data Collection

It is now possible to pass parameters to a simulation set up with data collection by appending them to the URL for the model. Learn More

December 12, 2017 - Stella 1.5.1

Flight Sim

The behavior of models running in Flight Sim mode has been modified so that they respond continuously to input changes rather than momentarily pausing. Learn More

Parameter Control Panel

The functionality to create an import file from the Parameter Control panel has been updated to only save values that are changed. This will allow you to easily create import files based on optimization results and also to create an import file that captures a snapshot of the interface input control settings. Learn More

Context Sensitive Help

Context sensitive help is now available in most dialogs as well as the properties panel.

November 21, 2017 - Stella 1.5


Optimization allows you to find a set of parameter values (model constants) that maximize a payoff you defined in terms of other model variables. This is similar to running sensitivity that is guided to achieve specific outcomes. Learn More

Confidence Bounds, Histograms and Correlation Plots

The output of graphs and tables has been enhanced to support a number of formats that can be very helpful when working with a large number of sensitivity runs.

Confidence bounds allow you to see what percentage of runs leave values in different ranges at each point in time. This allows for a clear visualization of the divergence or convergence of values over time given different assumptions on parameters and also how concentrated the values are at any point in time. See Graph Series Property Panel for details on turning these options on. The same information can be presented in tables identifying numeric values for the different percentiles (see Table Properties for details).

Histograms are created by collecting results from different runs and grouping them into buckets for different ranges. This allows you to see how many runs fall into each of the ranges. Histograms are available as an option on the Bar Graph. Learn More

Correlation plots allow you to see how one variable correlates with another over a series of runs. This is done with scatter graphs by turning on comparative and checking the option to show only a single value. Learn More

Precomputed Values

When a model is paused, the values of all variables, stocks, flows and converters, are available at the time of the pause. On the model window these values will be updated if you make changes to any model parameters. For tables and graphs, the interface will report only stocks at the current time, but other output devices, such as numerical displays, can be set to report the precomputed values. The option to pause before computing flows has been removed as this is no longer necessary. Learn More

Sensitivity, Payoff and Optimization Setup

These are now accessed through the model analysis tab of the properties panel for the model. Use the sensitivity tab to access sensitivity setup. Learn More

Context Sensitive Help (not in rc1)

Clicking on the ? icon in any of the panels or dialogs will now take you to the help entry specific to that panel or dialog.

Save Interval

You can now specify a save interval. This is useful for decreasing the storage requirements for large models and also for keeping data collection working well. Learn More

Graph and Table Labeling and Ordering

If you are using the tabbed or dropdown styles for selecting between multiple graphs you can now set a label for the tab or dropdown entry that is separate from the graph/table title. It is also possible to reorder the entries. See Pages Styles (Interface), Graph Settings Properties Panel, and Table Properties for more discussion.

September 29, 2017 - Stella 1.4.3

Keyboard Shortcuts

You can now use keyboard shortcuts to select tools when building models. Select the Stock tool with "Ctrl/Cmd + 1" and so on. Learn More

September 22, 2017 - Stella 1.4.2

Graph and Table Pad Labels

You can now rename the graph and table pads that show when the graph or table is minimized. Editing works just as it does for variable names.

Annotation Button for Variables

You can now use the annotation button to display a variable's documentation, equations and units of measure. Learn More

Graphical Panel

The units of measure now appear in the graphical panel - making it easier to there are units issues with graphical functions. Also, if the equation for a graphical has an error the panel will open on the equation instead of the graph.

Interface Page Resizing

When setting interface page size, existing content may restrict how much it can be adjusted. If a page has content that would be outside the page on resizing you will not get a message indicating the reason the page size was not able to be changed as requested.

July 10, 2017 - Stella 1.4.1

Loop Label

A new Loop Label object has been added to the mode editing toolbar. This allows you to label loops and will highlight the links in the loop when the mouse passes over it. Learn More

Navigation on the Model

A new navigation button has been added to the model to allow position changes to predefined locations or variables. These can be useful as shorcuts for navigating through large models. Learn More

New Builtins

Use NAN to set a variable value so it will not appear on graphs. Use CLOCKTIME to return the current time on the computer the software is running on. Learn More

Graphics Frame on the Interface

There is now an option to fit the graphics content to the frame. Learn More

July 22, 2017 - Stella 1.4

Multiplayer Games

In addition to publishing model interfaces, you can now create multiplayer games in which players connect from their own browsers, make decisions, and indicate their readiness to proceed. The model then uses decisions from all of the players as inputs for the next step in the game. Multiplayer games can be published to the isee Exchange under the Creative Commons license, with some limitations on model size. Learn More

SVG Animations

It is now possible to create sophisticated animations based on SVG graphics files. These animations can include color, size, and rotation. Learn More

Conditional Actions on Buttons

When you add a button to your interface, you can now set conditions under which each of the actions will be executed. This is especially useful in multiplayer games. Learn More

Resizeable Interfaces

Published interfaces can now be made resizable, allowing them to work well on a variety of devices. Learn More

Data Collection

You can now collect data on the use of your published simulation, including the results from different users and the time spent on different pages. Data collection is available through an isee Exchange subscription. There are several reporting options available for analyzing the data. Learn more .

Array Expressions

The modeling language has been extended to allow the use of expressions inside of the array functions (such as SUM(a*b)) to take an inner product. An inner product operator has also been added for 1 and 2 dimensional arrays. See Working with Arrays and especially Specialized Array Manipulation for more discussion.

Multiple Page Graphs, Tables, and Inputs (Interface Only)

Here are new options for navigating through multiple pages of graphs, tables, and input devices. Rather than the standard right and left buttons, you can use tabs for each page, or a dropdown list including all pages. This is applicable to graphs, tables, group inputs, and arrayed inputs, and is selectable from the properties panel for each. Learn More.

Connecting Modules

When you connect a variable to a module, or a module to a variable, you will see a menu item allowing you to select which variable within the module to connect. This will appear only if there is something marked as an input or output within the module that has not yet been connected.

Using Initial Equations with Graphical Functions

We have made a behavior change when you are using a separate initialization equation for a graphical function variable. Previously, the I equation would determine the value of the variable. Now the I equation determines the input into the graphical function.

Initialization and Graphs

Graphs will now use the initial values computed in the background. For bar graphs and pie charts, this means they will be populated with initial values before and after running an output restore. Regular graphs will not draw, but they will have a scale. This is true for models and interfaces, including published interfaces. Note that changing a controlled value will no longer generate a new initialization.

Stella Live Behavior

We have adjusted Stella Live to be less sluggish on larger models, and also to give visual cues when the model is in the process of computing. In particular, as you dial a knob, while the software is computing the graphs, over model elements will be displayed in gray instead of red. This indicates that the graphs are potentially out of date relative to the value showing for the knob.

June 12, 2017 - Stella 1.3.1

Model Editing

If you try to make a connection that would cause a circularity the list of variable involved in the circularity is not displayed in a dialog box.

Hovering on a connecter into or out of a module will now show which variables are being connected.

You can now navigate out of modules using keys. To get to the containing module use Ctrl+Up Arrow (⌘+Up Arrow on the Mac). To get to the home module use Shift+Ctrl+Up Arrow (Shift+⌘+Up Arrow on the Mac). Learn More.

The three line limitation on variable names has been removed.

You can now add polarity symbols to flows.

Interface Editing

On the interface, the auto-alignment grid now includes objects in templates so that you can more easily manage page layout.

Keyboard scrolling using the arrow keys has been improved.

Equation Editing

Array names and elements have been added to the auto-complete when working with arrayed equations.

The scales and ranges tab has a new icon (#) that is more representative of its function.

Published Models

We have substantially improved the performance of published models of significant size.

May 10, 2017 - Stella 1.3

Stella Online

You can now edit and work with your models online by logging in through the isee Exchange. Learn More

New Graph Options

Available for both the model and interface we have added two new options for displaying results. The Pie Chart is a new output format for the display of variable values at a point in time. The Area Graph allows you to display a series of graph values stacked on one another with distance between them based on the values of the variables. Both of these are configurations of graph objects and can be selected in the Graph Properties Panel.

Allocation Input on Interface

The new Allocation Input (Interface) object allows users to set values for inputs that need to add up to a set amount. It is implemented as a draggable pie chart, with adjacency determining the sequence in which other inputs change as the user makes adjustments.

Reset Buttons on Interface

A reset button has been added to interface input objects allowing them to be reset to the model value by the user (the button also marks the control as changed). This option to use this is set in the Interface Settings Properties Panel.

Import/Export Now action on Interface

Buttons on the interface can now execute either an import or an export of an on demand data link. These actions do not do anything for published models. See Button (Interface) for more details.

Graphical Input Points

Graphical input objects on the interface can now be changed either by tracing the shape, or by switching the Table view and entering xy pairs. Learn More.

Improved Import and Export Capabilities

You can now import both the x and y axis for graphicals by putting :x and :y after then name of the graphical in successive rows or columns. See Creating Import and Export Files for details. The import options now handle arrayed inputs more consistently and better manage compatibility between US and European number formatting.

Parameter Control Panel Improvements

The Parameter Control Panel now highlights variables that have been overridden on the panel making it clearer what has been changed (this is especially important for values already imported).

Language Changes

Any graphical functions that use a constant as an input will now be marked as invalid. This makes it easier to uncover issues where TIME might have been the intended input. If you do want a constant as an input you can use an expression (as in 0+0) to prevent the error. The INIT and ENDVAL builtins can now take an expression in addition to using a variable directly.

February 1, 2017 - Stella 1.2

Updated Data Manager

A number of other improvements have been made to the Data Manager giving you more control over the way in which runs roll off the list and what runs are displayed in graphs and tables. Learn More

Importing External Runs

We have added the functionality to import runs from external data sources to the Data Manager. This makes it easy to compare results with measured data or with results from other models. Learn More

Parameter Control Windows Updates

The parameter control window has been enhanced so you can see the original model value and to make it easier to reset and control different variables. Any variables appearing in the parameter control window are also marked on the model diagram.

Model View Improvements and Animation

You can now optionally animate diagrams shown in the Model View including those shown for storytelling. The Model View controls have been improved to make it easier to include model elements on interface pages and stories. Learn More

Circularity Checking

Circularity checking and reporting have been improved and now detects subtle initialization dependencies related to leakages and discrete stock equilibrium initializations. Circularities are now reported one loop at a time, and all the variables in the loop are marked invalid making it easier to visual the loop.

Divide 0 Operator

We have added a // operator which works the same as SAFEDIV giving 0 instead of an error when dividing by 0. Divide by zeros are more accurately reported, even when they occur within expressions such as MIN. Legacy models will automatically have some of this reporting masked to maintain compatibility.

Preserving Graphs and Tables

You can now preserve graphs and tables with a single click so that they will not change with new runs or be cleared when you restore outputs. This is done from the Graph Properties Panel. Learn More

June 20, 2016 - Stella 1.1

Interface/Stella Designer

The interface development tools are all new. The new interface development and deployment capabilities take you from design to presentation and, optionally, the web quickly and cleanly. Learn More

Interfaces developed in previous versions of the software will be translated and most of their functionality retained, though some adjustment will be necessary to get optimal results. Learn More

Causal Lens

The Causal Lens displays graphs for a variable and the inputs to that variable helping you to better understand the sources of model behavior. Learn More

Table in Results Panel

The Results Panel now includes both a graph and a table allowing you to look at specific values at specific times easily. There is also a checkbox to not round the scales which is helpful when looking at variables with limited movement through a simulation. Learn More

Simulation Log

The Simulation Log records any variables that go above or below their specified ranges, as well as graphicals with inputs above or below their specified minimum and maximum x values. The same log is also used to report messages about anything that happens when opening a model. Learn More

Parameter Control

The Parameter Control Panel allows you to see what variables are changed relative to their model equations, and also make changes to those variables. Learn More

Selection History Panel

The Selection History panel keeps track of which variables you have selected making it easier to go back and see where you have been. Click on an entry till take you back to that variable. Learn More

Clearer Selection Highlighting

We have improved selection hightlighting to make it easier to see which variables have been highlighted. This is especially useful as we have added a number of new ways to navigate between variables.

Causes and Uses in Equation Panel

You can right click on a variable in an equation and jump to that variable. There is also a Causes/Uses menu to navigate to variables that cause, or are used by the variable you are looking at. Learn More

Improved Error Messages

We have improved the error message reporting in equations and made this reporting somewhat stricter, especially around the MIN and MAX functions, to prevent ambiguity.

More Informative Units Messages

The units messages now tell you have many variables you have left to define units for. If you have not defined units for any variable, the dropdown simply reads Define Units.

Unrestricted Naming for Variables

There are no longer any restrictions on what names you use for variables, except that they must be unique and not conflict with any Builtins. When used in equations variables that have operators or other characters will be quoted and escaped. (If you type them in you will need to do this, but it happens automatically if you choose them or use autocomplete.) Variables with a period (.) in them will also be quoted when displayed on the diagram (this is to prevent confusion with module qualified names).

Improved Speed

Models open significantly more quickly than before letting you get on with development. Exporting of data is significantly faster and will happen in parallel during simulations.

Added PROD Functions

An analog to the SUM function takes the product across elements of an array.

Large Model Use

An option has been added to the Preferences Dialog that turns off Stella Live when in Explore mode. This allows you to work with larger models and make changes on the model window but only simulate them when you explicit request a run. Learn More

Run Specs always Available

You no longer need to go to the home module to change run specs or other model wide settings. These are avilable in the panel from any module.

Equation Viewer

You can now order equations by sector and also view values in the Equation Viewer. Complete information about model size has also been added to the end of the equation listing. Learn More

Simulation Events

We have redone what used to be called Posters or Simulation Messages into an easier to use system of Simulation Events that can be applied separately to the model and interface. Existing models will have these converted to the new format working on the model. Navigation events will need to be redone. Learn More

Export Formats

We have added new export formats to export a single set of values or values at a time and improved the way tables are specified for exporting. Learn More

December 8, 2015 - Stella Professional 1.0.3

Integration with High Resolution Displays

Version 1.0.3 is designed to work well with high resolution displays, including Retina displays on the Macintosh. The icons on the screen will automatically be enlarge to accommodate displays with high pixel counts and the diagrams will be presented so that it is easy to read at default zoom levels.

Updated Icons

We have updated the icons used throughout to be clearer and more consistent in addition to working better on different resolution monitors.

Edit Explore Transition Changes

The movement back and forth between Edit and Explore modes has been streamlined. Changes you make to constants in explore mode by adjusting knobs or entering values in the Results Panel will persist if you enter Edit Mode and then go back to Explore Mode. Modifying an equation will reset any value you set in explore mode, but only for that equation.

Enter values for arrayed constants in the Results Panel

You can set values for arrayed constants in the Results Panel in explore mode (arrayed constant do not have adjustable knobs). Just open the results panel and click on the constant you want to change. You can select the array entry to change from the dropdown at the top of the results panel.

Increment setting for constants

Constants now have an increment setting that can be used to control the number of values they will take on when changed via a knob in Explore Mode. This can be very helpful if you want to limit the number of values that a constant can take on, and will even allow for the addition of switches that take on only 0 and 1 as values. The increment is set in the Scales and Ranges panel.

October 12, 2015 - Stella Professional 1.0.2

Importing Temporary Changes

This functionality has been moved to the Panel to make it easier to use. Rather than opening the import dialog, open the Properties Panel on the model and there is a new tab to make temporary changes, including importing interface settings from STELLA and iThink Version 10.1.2 models.

Graph and Table Creation

Clicking on the add variable button in the graph and table panels will now open up the Find dialog making it easier to select and add variables.

Improvements to Copy

Copying model diagrams into the clipboard is now more sensitive to context and will remove the borders from graphs when they are copied by themselves. This makes it easier to paste your content into other applications.

Map/Model view stored with model

Now when opening a saved model, it will open in the same view in which it was saved.

August 6, 2015 - Stella Professional 1.0.1


Substantial improvements have been made to Stella Professional's computation engine. Not only will models open more quickly, but large models should simulate three to eight time faster than in the previous version. This allows you to get more done more quickly.


A new function SAFEDIV (<numerator>, <denominator>, [<onzero>]) has been added that allows division in cases where the denominator might become 0. When this happens the function will return 0 or the optionally specified third argument. Use this to prevent simulations stopping because of a divide-by-zero condition. Learn More

Importing Temporary Changes

The Import functionality has been enhanced to allow you to import values without making any changes to model structure. This is useful for running experiments in which you do not want to change the model, but just see the results of changing constants and graphical functions. This also allows you to override computed variables with a constant value, much like you would when, for example, attaching a slider to a converter on an interface.

An option has also been added to the Import dialog that will read interface control values from a model created in version 10.1 and create a temporary change files. This allows you to simulate models in Stella Professional and get the same results that they generated in the Version 10 products.

Repeating Build Steps with the Alt Key

The Alt key now works by holding it down, rather than tapping it, when you want to repeat a build step such as drawing connectors between variables.

Clear Highlighting of Connectors and Names

When you position the mouse over a connector handle (or arrowhead) the color of the connector will change to indicate that it is active and can be dragged. Similarly when you position the mouse over a variable name, the name will be highlighted with a box to indicate it can be repositioned. This makes it much easier to adjust model layout, especially for densely connected models.

New Menu Items

A Windows menu has been added to allow you to more easily navigate between models when you have multiple models open. Under the Windows menu is an item to open the Results Panel. A Run Specs menu item has been added to the Model menu as an alternative way of opening the Run Specs panel.

Registration Dialog

Registration information can now be accessed and changed through the Registration dialog box opened from the Help menu. This allows you to change your registration information and unregister the software from one computer, so you may use it on another. Learn More

Delay Marks and Lettered (s/o) Polarity

When you place a connector the Style Panel will contain an option for a Delay Mark. The polarity markers can be shown using either +/- or s/o as specified in the Model Settings Properties Panel.

Hide Module Prefix Option

Set this on the Model Settings Properties Panel to shorten the names displayed in graphs and tables (eg. have profit be displayed instead of accounting.profit). Learn More

Sketchable Graph Enhancement

You can now create a Sketchable graph for any graphical function in the model without needing to add another variable for comparison. This allows you to use the Sketchable graph as an input control. Learn More

March 26, 2015 - Stella Professional 1.0

The Stella Window

While using the same set of building blocks and supporting you step-by-step in maintaining the integrity of the models you build, you now have more flexibility and control over appearance. You'll also find powerful new ways to work with and understand your models.

New Toolbars

For previous users, Stella Professionalis both very familiar and very new. The first thing you notice is a new set of toolbars.

Build Toolbar

The Build Toolbar contains the same components as previous versions, with slightly different icons. By default it is in the same location.

Moving Toolbars

All toolbars are movable and can be docked on any side of the window. By default, the Build and Mode toolbars are at the top, and the Run toolbar is at the bottom. If you grab the handle at the left end of a toolbar, you can put the toolbar in a new location along one of the other edges, or leave it floating.


Side-docked panels allow you to define and edit properties for model entities while still viewing the diagram. Drag and drop entities from the diagram into equations to use them as variables. Undock the panels to create a floating window that you can resize and place anywhere on your screen. Learn More


In addition to fonts and colors you can now set the size on stocks and converters and set specific Converters to be name-only. This, combined with bendable Bezier connecters, allows much more flexibility in presentation. Easier layout is facilitated by Object guides. These appear as you move objects around the window, any time one object aligns with another.


You now have much more control over appearance. Set fonts, colors, and other attributes. For example, you can change the font on flows, mark a converter as Name Only, resize stocks, and use Bezier connectors

Model Hierarchy

Run Specs and Page Settings follow this heirarchy, and are set from the Properties panel. When in the root page of the model, with nothing selected, set the Run Specs and Page Settings for the entire model. If you create new modules, they inherit those settings, but you can override them for any module. Any modules used within that module inherit its properties, but they in turn can be overridden.

Partial Simulation

Use Partial Simulation tab to select specific modules or sectors to include in the simulation.

Page Settings

Use the Model Styles tab to set default fonts, colors and label positions for all objects for which those attributes have not been set.

Run Specs

Models use a hierarchical structure. Set styles for objects at the model level and override them at the module or object level. Change the model style to changes everything that has not been explicitly overridden. You can also change styles and other attributes for all selected objects.

Multi-dimensional arrays

Expanded array capabilities provide more flexibility when you are defining array equations, creating arrayed graphical functions, and entering constants across an array. Create up to ten dimensions for arrayed entities. Index dimension elements by number or label. Use the new Array Editor to easily import or paste element labels from a spreadsheet or comma/tab-separated list. Learn More

Data Manager

The new Data Managers allows you to archive and recall simulation results. Name and save run data from different scenarios or sensitivity tests to easily identify and reload results. Simulation data is stored in a separate SQLite database file and accessible using standard database tools. Learn More

Embedded modules

Hierarchical modules are now embedded in a single model file by default. For collaborative model building and creation of reusable templates, use the option to automatically save modules as separate files. Learn More

Statistical built-in functions

COMBINATIONS, FACTORIAL, INVNORM and PERMUTATIONS have been added to the list of statistical built-in functions. New stochastic distributions include BETA, BINOMIAL, GEOMETRIC, GAMMA, LOGISTIC, PARETO, TRIANGULAR, and WEIBULL. To learn more, see Statistical builtins. Learn More

Rich text documentation

Source information and other details about model entities can be documented in rich text/HTML format, using options available in the new Documentation panel. Learn More

Improved conveyor leakage

Conveyors now support multiple leakage flows. Use additional leak zone options to simplify main chain structures that contain cohorts with varying leakage fractions. Learn More

Expanded Find functionality

Use the new Find palette to locate model entities using string search, hierarchical views, and filtering capabilities. Drag and drop entities from the Find palette directly into entity equations and input/output devices. Learn More

New graphical function options

Edit the input values (X-axis) of graphical functions to align with your data. Use the new continuous extrapolation option to linearly extrapolate values that are beyond the graphed curve. Learn More

Industry standard XMILE format

Model files support the new industry standard (XMILE) for common interchange of system dynamics models. Use any text or XML editor to search, edit, or document your model. Learn More

More powerful modeling engine (STEAM)

The new STEAM engine does not place limits on the number of entities, data points, and/or time steps in your models. This new more powerful and flexible engine will provide a solid foundation for future development and expanded functionality of Stella.

Cycle Time

Cycle Time lets you time stamp and track material as it flows though the model in order to precisely compute how long different tasks and activities are taking.

Delay Converters

Delay Converters lets you mark a Converter as changing over time in response to changes in its input as happens with SMTH1, SMTH3, DELAY, DELAY3 and related Builtins. A Delay Converter shows a box inside the regular Converter circle indicating it has some of the properties of a Stock. Because it has properties of a stock it is possible for Delay Converters to be involved in feedback loops in which no explicit Stock exists.


Units are more flexible and comprehensive and provide better feedback on issues in dimensional consistency. It is now possible to define multiple aliases for a unit of measure so that you have more flexibility in expressing compound units.


Sensitivity now allows for a broad range of distributions in specifying input changes.

Module Files

Module files are now stored in a folder prefixed with the model name so that you can save a separate copy of a model using modules in file without changing the original model.

Find Dialog

Find dialog has been updated to provide much better control for searches including finding remaining Building Block errors.

Random Number Generator

New Random Number Generator provides more robust streams of values for the different random number Builtins. The new generator is appropriate for use with high replication Monte-Carlo.


New Builtins have been added, primarily to support Cycle Time (CTFLOW, CTMEAN, CTMIN, CTSTDDEV, CYCLETIME, THROUGHPUT) but also UNIFORM for random number generation and GAMMALN for statistical computations.

Arrayed Equation Editor

Arrayed Equation Editor for non Apply-to-All arrays makes it easier to work with arrayed variables that have multiple equations. You can pop it up from the Equation tab of the Properties panel and select multiple element entries to edit together. This makes it much easier to work with arrays where many of the equations are the same.

Explore Mode

Enter Explore mode by running the model from the Run toolbar or menu, or select Explore from the View toolbar. In this mode, graphs appear on all objects for which results are available. To view larger graphs, including full axis labeling, open the Results panel and select an object containing a graph. This allows you to easily walk through a model with the mouse looking at results. Open the Results panel from the Model menu or right-clicking an object and choose View Results.

Edit Mode

Enter Edit mode by double-clicking a model element while in Explore mode. All appropriate tabs appear for the selected object.

Validity Indicators

The validity mechanism evaluates equations and units for validity and dimensional consistency. In Map view, any unfinished or invalid building blocks contain a small caution sign.

Results Panel

The Results panel shows comparative graphs on-the-fly. You can still define and place Graphs and Tables in the model with these added capabilities to graph any selected variables from selected runs, include comparative and non-comparative results in a single graph or table, use the Properties panel to control scaling, layout and appearance and Ctrl-Drag (Cmd on Mac) building blocks onto output devices to populate Graphs and Tables. You can even use this method to populate equations, summing converters, and any input variable.

Comparitive Graphs and Tables

Comparative tables and graphs now work in concert with the Data Manager. Any runs held by the data manager are displayed in Comparative graphs and tables as soon as you specify the variable. Thus you do not need to run the model again to see the results when you change a variable. If you have specified that 5 runs be saved in the Data Manager, the oldest run falls off of Comparatives when you make a sixth run. When doing a Sensitivity run, Comparative graphs and tables show the results for all of the Sensitivity runs, but once you make another run, they revert to showing the runs stored by the data manager (which may be a smaller number of runs). You can now lock individual runs in graphs and tables. This can be done on the Property panel for the graph or en-masse for Comparatives by right clicking and accepting the list of Displayed Runs other then Next Run.

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