Feature Updates

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May 10, 2017 - Stella Architect 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 to 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. 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 Architect 1.2

Improved 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 Architect 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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