Negative Levels
Posted: Wed Oct 09, 2019 6:36 pm
I have been using VenSim PLE for about ten years now in teaching a Modeling Calculus course. This is a course in which we teach Euler's method and Runge-Kutta and modeling with differential equations. Every now and then a new feature is added to the software that causes some small problems I need to account for. (The last time this happened was when you dropped Euler's method as an option for computations.)
In the latest version (8.0) it appears that it is impossible for levels (AKA box variables) to take on negative values. I run models for the equations of motion, and I like to demonstrate the need for using inequalities for testing values. (i.e. you can't test when height = 0, you must test for height <= 0) Additionally, I give abstract differential second order differential equations, just to demonstrate stability of solutions and other analysis of solutions. Now there is some change in the latest version where if the level becomes negative, a value of zero is given.
It is my hope that there is a setting I can change to allow for negative levels.
Brian Birgen
Wartburg College
In the latest version (8.0) it appears that it is impossible for levels (AKA box variables) to take on negative values. I run models for the equations of motion, and I like to demonstrate the need for using inequalities for testing values. (i.e. you can't test when height = 0, you must test for height <= 0) Additionally, I give abstract differential second order differential equations, just to demonstrate stability of solutions and other analysis of solutions. Now there is some change in the latest version where if the level becomes negative, a value of zero is given.
It is my hope that there is a setting I can change to allow for negative levels.
Brian Birgen
Wartburg College