SyntheSim is a new and unique Vensim capability.
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. 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.
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. A dialog will open allowing you to override the behaviour of the variable.
To see a demonstration of SyntheSim, go to the downloads page.