Using discrete functions

[Monte]

Hi Bob,

Vensim provides a variety of useful discrete functions, but I found many of them hard to be used, because I cannot draw flow diagrams appropriate for those functions.

In detailed function description, if the Vensim manual will also give flow diagrams in addition to the existing text, it will be much more helpful.

Have you ever created flow diagram for all functions available in Vensim Pro? I would be pleased if you could let me access them.

Happy new year to you all.

Monte

[bob@vensim.com]

Hi Monte,

Discrete functions are not part of the paradigm of system dynamics and therefore do not have any standard stock and flow representations. For example the delay fixed could be represented by inflow, Level, outflow but would then look like a smooth function which would not be so good. Sometimes a series of Vertical bars are drawn through the level, but that is also down for 3rd order continuous delays.

So no such diagrams exist, though some people adopt conventions for use in their own diagrams.

[Monte]

Thank you for your help. When using Vensim functions, ones must enter equations into the "stock-flow diagram" in the drawing area of the software. I am looking for such flow diagrams that need not to be standard, but that must be created before we can use the functions in Vensim.

I would like to practice all functions provided in Vensim, by constructing theoretical flow diagrams, entering equations (with functions), and seeing the behaviors of such functions. Examples of Vensim flow diagrams, if available, would make it easier (or possible) to learn how to use each function that is not common.

[bob@vensim.com]

There is a chapter in the modeling guide on discrete functions - this has some example presentations. The rules are the same for any other function use eg

input --------------> output using delay fixed

but the meaning underlying the relationships is different.

[Monte]

I'll read Chapter 9 carefully. Thank you.