Review

UniServe Science News Volume 8 November 1997

Powersim 2.5C

Powersim is an object-oriented package for the construction of interactive simulation models.

"This is the first laboratory session on simulation modelling. Let us construct a model of a drainage system. We will begin by creating a rainfall input sub-model with a Monte-Carlo distribution of n rain-days per year, and a log-normal distribution of rainfall amount on the rain-days."

That statement is typical of the way I do start my sessions on simulation modelling. Using Powersim, the above task is accomplished by positioning one screen object, and, with the aid of built-in functions, inputting a fairly straightforward equation. Add a graph using drag-and-drop methodology, and one's students may then run the sub-model for a year of simulated time and see the rainfall pattern develop, all within minutes of commencing the practical session.

Powersim is one of several object-oriented packages available which allow rapid construction of simulation models in a systems dynamic framework, using visual objects, point-and-click, and drag-and-drop techniques. A powerful heuristic feature of these packages is that they allow for the on-screen construction of a flow-chart style representation of a model, in much the same way one would develop a conceptual flow chart on paper before writing a model in a programming language. But this is where the similarity to conventional programming ends, for, having constructed the on-screen flow chart in Powersim, one has only to add the governing equations in order to begin a simulation. The package thus allows users to concentrate on the intellectually stimulating and creative aspects of simulation modelling, and skip the tedium and frustration normally associated with the process. Other examples of the modelling genre are Optima!, Simul8, Dynamo, iThink, STELLA, and Vensim. The author has some familiarity with all of the latter packages, with extensive experience of STELLA and iThink. Indeed, for some time STELLA was used for all of our classes on simulation modelling. However, our Department has changed over to Powersim, for a variety of reasons, most of which have to do with its excellent range of features, such as:

• Powersim has the capacity to toggle between two levels of utilisation, with a simplified user interface that allows beginners to learn in a non-threatening and relatively uncomplicated environment whilst at the same time actually using the full strength product. Any work done in the simplified environment does not have to be re-done to run in the fully featured environment, and models constructed in the latter may be run in the simplified environment.
• Powersim has over 150 built-in functions (about twice as many as STELLA)
• Powersim has a wide variety of objects for the presentation of simulation results: two-dimensional X-Y graphs, histograms, one-dimensional by time graphs, speedometer style gauges, simple numeric display, or tables. Add to this the capacity to readily import illustrations, and one may construct a display interface (complete with slider buttons to alter inputs whilst the simulation is in progress) on one page of the model, with all of the "plumbing" on a second page.
• For serious users, Powersim supports Dynamic Data Exchange (DDE) using standard Windows protocol (essential if one wishes to calibrate one's model with reference to real-world data stored in a spreadsheet, say), and also boasts an Application Programmers' Interface (API) which allows programmers to connect Powersim applications to programs developed in C++, Visual Basic, or Delphi (for example, one may wish to employ Powersim as the simulation "engine" in a model which does not have simulation as its main function).

In the retail market, Powersim is somewhat more expensive than the other products mentioned, but for educational users, there is little difference in price. Some colleagues may also be interested to know that, at the time of writing, cross-upgrades to Powersim are available at an attractive rate. To download demo: http://www.powersim.no/

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