Release Notes for Stella 1.8.3

These release notes list feature changes for the current release of Stella Architect, iThink Version 1.8, Stella Professional, and Stella Designer. Feature changes are also shown for previous versions of the software. There is a list of Known Issues for the current software release as well as a version by version detailing of Defects Fixed.

New and Updated Features

In 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.

In 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 variable 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.

In 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. See Team and Role Assignment for more discussion.

SENSIRUNCOUNT Builtin

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. See Miscellaneous builtins for details.

Allow use of SELF in ENDVAL

The SELF builtin can now be used in the ENDVAL builtin, allowing customized definitions of RUNCOUNT. See Data builtins

for more discussion.

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. See Graph Settings Properties Panel

In 1.8

Calibration

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. For more details see Calibration for more discussion.

Importing Time Varying Values

Time varying values allow you to have variables take on different values at different times based on 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. See File Menu

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. See Sensitivity Specs Panel for more details.

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. For details see Data Manager

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. See Working with Macros for more discussion.

New INTERPOLATE Function

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. See Array builtins for more details.

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. See Interface Settings Properties Panel for more details.

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. See Shape (interface) for more discussion.

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. See Graphical input (Interface) for more discussion.

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). See Slider (Interface) for details.

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. See Numeric Display Properties

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. See Loop Labels for more discussion.

Simplified Inclusion of CLDs

Causal loop diagrams created in The 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 equation. 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.

In 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. For more information see The CLD Window.

Switch Color

You can now set the color that a switch on the interface displays when it is on. See Switch (Interface) for details.

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. See Graphical input (Interface) for more detail.

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. See Allocation Input (Interface) for more details.

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. See Help Menu for details.

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. See Sharing Models Online for more discussion.

Causal Lens Improvement

If there are long variable names in the causal lens, you can now hover over them to see the full expanded name. See Causal Lens™ for more discussion of the Causal Lens.

Multiple leakages 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. See Conveyor Computation for more discussion.

 

In 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. For more details see Navigation Control (Interface).

Spell Check

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

Run by Modules Improvements

It is now possible to turn modules on and off in Stella Live, while paused, and on the interface, including in storytelling (see Running Modules for more discussion).

Conveyor Leakage Changes

Leakage computations on conveyors with a variable transit time have been improved to more accurately reflect the leak fraction or rate. See Conveyor Computation for a more detailed discussion of leakages and conveyor initialization and computation.

Encapsulating Sectors and Selections into Modules

Encapsulation allows you to take a selection of variables, or a sector, and automatically put them into 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. For more details see Encapsulating Structure.

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.

Improved Opening Time

Large models should now open more quickly.

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.

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. See Working with Macros for more details.

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. See Bubble Chart

for more detail.

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. See Scatter Graph for more discussion.

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. See Data Manager for more detail.

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. For more information see Stash Data for more discussion.

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. See Picture in Picture Module Viewing for more details.

Collapsable Panels

Many of the panels now include sections that can be collapsed if you do not need to refer to them. This decreases the amount of information displayed on the panel and thus easier to work with. See Stella Modes, Views, and Panels

for more details.

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. See Model Comparison dialog box for details.

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.

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. See Equation Viewer for more details.

Vertical Sliders

There is now an option to display sliders vertically as well as horizontally. See Slider (Interface) for more details.

Line Graph Updates

You can now specify that graph be drawn without connecting the points into line. See Graph Series Property Panel for more detail.

Button Highlighting on Mouse-Over (Interface)

There is a new option to have buttons change their appearance as the mouse cursor passes over them. See Styles Tab for details.

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. Details are available in Context Menu.

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.

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. See Loop Labels.

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. See Sensitivity panel for more details.

Improved Security Settings

We have made a number of internal improvements to the security settings (see Model Security dialog box) 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.

In 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. This is set up in the Sensitivity Specs Panel

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. See Optimization Specs for details on setting this up.

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. See Find window for more details.

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.

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. See Equation Viewer

for more information.

Sketchables with Fill

You can now fill in the area underneath a sketchable graph. This is especially useful when using discrete graphicals as it provides a sharp contrast between adjacent values.

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. See Sensitivity Parameters dialog for more detail.

In 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). See Window Menu

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. See Model Window Mode Toolbar for details.

View Results and Causal Lens

A combined View Results and Causal Lens has been added to the Online Model Editor. See Getting Started Online.

In 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.

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. See Scales and Ranges Tab for more discussion.

Time Formatting and Labeling

You can now format time to display years, months and days and not simply decimal values. See Setting up Time Bounds for more discussion.

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 sheeExport 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. See Simulation Speed for more details.

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. See Object Visibility (Interface) for more details.

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. See Display Time (Interface) for more details.

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. See the Model View documentation for details.

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. See Statistical builtins for more information.

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. See Statistical builtins for more discussion of truncation and sampling.

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). See Bar Graph for further discussion.

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. See Data Collection for details.

Behavior and Compatibility Notes for 1.6

Note that the BINOMIAL and GEOMETRIC builtins were not behaving the way they were documented. The probability parameter was being multiplied by DT prior to execution. If you are using these with a model that has DT of 1, there will not be any change in behavior. Otherwise, multiply the probability by DT to get the same behavior. The MONTECARLO builtin will also allow you to specify a success probability that is limited to 100% per DT, not 100%*DT per DT as it previously did.

Backward Compatibility

Models from versions prior to 1.6 can be opened and saved in 1.6 then reopened in previous releases and should be unchanged. As always, new features available in 1.6 will not be recognized in previous versions. Thus, for example, additional arguments to NORMAL and other random number generators will be treated as errors in earlier versions of the software.

The new time and number formatting options introduce more complexity when models are opened in previous versions of the software. By design, if a model from version 1.5 is opened and saved in 1.6 it will reopen unchanged in version 1.5. However, if you make changes to the default number or time formats (see below) in 1.6 then those changes will be lost when opened in 1.5. When reopening in 1.6, you will need to add back in the default format changes. As you add in additional number and time formatting options this becomes more complicated and it is possible to lose additional time and number formatting information. Therefore, if you are planning to work with people using prior versions of the software it may be simplest to not set the model level defaults for time and number formatting.