modelica: compute minimum/maximum of continuous variable over time

Question

As stated above: I wish to compute the minimum (and/or maximum) of a continuous variable over time. Here is a minimal example to demonstrate:

model MinMaxTes         


        

Answer 1

For your initial question, what seems to work correctly for me in OpenModelica is this:

u_min = min(u, pre(u_min));
u_max = max(u, pre(u_max));

For me that compiles, simulates, and gives the expected results, but also does say "Matrix singular!". On the other hand, if I change the initial declaration for u_max to this:

Real u_max(start = 0);

Then, the "Matrix singular!" goes away.
I don't know why, but that does seems to do the job, and I would suggest is more straightforward then the other options you have listed.