With Vensim 5 you can synthesize model structure and simulation behavior - we call this feature SyntheSim for Synthesis of Simulations. Vensim allows you to see the results of simulations superimposed on the model diagrams and instantly updates these displays as you change model Constants and Lookups. SyntheSim requires a simulatable model, but you don't need to do anything special to it. Just click on the SyntheSim Icon (
) or select SyntheSim from the simulation control dialog. Once you do this you will see small graphs over all dynamic variables and sliders will be created for all the constants. As you move a slider the model will be simulated and the graphs automatically drawn.
You can also view behavior without entering SyntheSim mode by selecting the Show Behavior menu item on the View menu. This will display whichever runs are loaded and can be left on as you build and make adjustments to the model. This is also useful for very large models that are too big to use in SyntheSim mode.
SyntheSim Options:You control the behavior of SyntheSim graphs from the Scaling Tab of the Control Panel. Colorize, if checked, will cause SyntheSim graphs to flash Red when the scale is expanding and Blue when it is contracting. Freeze, if checked, will cause the scales to stay unchanged until the mouse button is released. Include 0, if checked, makes sure that 0 is in every SyntheSim graph. Finally the Buffer Mult determines how much rescaling occurs when it is necessary to expand the scales as well as the threshold for contracting the scale. For big models there is an option to prevent simulation except on button releases. This is set from the Sketch Appearance tab of the Model>Settings dialog.
Changing Structure (Not in PLE):In addition to making changes to Constants and Lookups SyntheSim makes it very convenient to cut feedback loops. Just pick a variable that you would like to change and click on it with the right mouse button (or Control-Click on it). A dialog will open allowing you to make changes.
Uncheck Override normal behavior to have the variable revert to normal behavior, or select one of the Input TimeShapes desired. Note that any variable can be turned into a constant with a slider, but this selection will be grayed for constants since this is their normal behavior. Depending on the type of shape you will also need to parameterize the shape.
You can make the variable behave like a constant, or force a time pattern of behavior on it. You can also use this technique to turn constants into time varying inputs.
Check on the Freeze Levels at initial values button to study the local responses (no feedback) to variable changes. You can change the behavior of as many variables as you wish.
Runs:The SyntheSim graphs display values from all the loaded runs. You can load, unload and reorder runs from the Control Panel at any time. If you want to keep the currently displayed results just change the run name to begin storing to another dataset. As you type in the run name you will see a marker if the run name you are typing matches an existing run name.
Subscripts:For subscripted variables the subscript element displayed is determined by the first selected subscript in the Subscript Selection dialog. As you change the subscript selection the values displayed will change.
