An interactive system for the construction and animation of systems dynamics models

An interactive system, SIMILE, for the construction, manipulation and animation of systems dynamics models is described. The system is intended to be used primarily as an educational tool, to allow users to experiment with and develop systems dynamics models. However, the system also may be used for creating films of these models.

A model is represented pictorially as a graph, where nodes represent components and edges show relations between these components. One is able to graphically create and modify a particular model. In executing or running a model, the graphic configuration is itself animated; this animation may take place at a display terminal, or the system output may be routed to a microfilm plotter to produce a film of the model.

At the terminal, the execution may be speeded up or slowed down; also one may step through the model (with respect to time), or examine the state of the model at any point in the simulation. Plots of the values of selected variables against time may also be obtained. In addition, changes to a model, or in a model's parameters, can be easily made and the effects of these changes can be immediately seen.

A number of short films have been produced by the system. These include a film which illustrates certain aspects of feedback loops and another showing the effect of specific parameters on a model of an influenza epidemic.