Release Notes for Stella 1.5.2

These release notes list feature changes for the current release of Stella Architect, iThink Version 1.5, 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 1.5.2

Version 1.5.2 contains defect fixes only, and no new features.

In 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. See Flight Sim Mode for details.

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. See Parameter Control Panel for more details.

Context Sensitive Help

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

In 1.5

Optimization

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. See Optimization for more details.

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

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. See Graph Series Property Panel for details.

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. For more information see Initialization and Pausing. The option to pause before computing flows has been removed as this is no longer necessary.

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. See Sensitivity Specs Panel for more detail.

Context Sensitive Help

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

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. See Model Settings Properties Panel for more information.

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.