OMPython/OpenModelica setMethods

Question

I am trying to change parameter with setParameter in OMPython where I have loaded Modelica model and solved it. I want to change parameter with other numerical values but getting error message:

| info | setParameters() failed : It is not possible to set the following signal "Nass", It seems to be structural, final, protected or evaluated or has a non-constant binding, use sendExpression(setParameterValue(CyclicLoading, Nass, 12000), parsed=false) and rebuild the model using buildModel() API

OMPython code before setParameter introduced:

from OMPython import ModelicaSystem
from OMPython import OMCSessionZMQ
omc = OMCSessionZMQ()
modelpath="C:/work/code/modelica/"
Nom_fichier_mo="CyclicLoading.mo"
Nom_fich="CyclicLoading"
fich_res_Modelica_mat="Resultat_av_CyclicLoading.mat"
mod=ModelicaSystem(modelpath+Nom_fichier_mo,Nom_fich,["Modelica","CyclicLoading"])
mod.buildModel()
Directory_cd=omc.sendExpression("cd()")
resultatSimluation=mod.simulate(resultfile=f"{fich_res_Modelica_mat}")
Solution_var=mod.getSolutions()

OMPython code after setParameter introduced:

from OMPython import ModelicaSystem
from OMPython import OMCSessionZMQ
omc = OMCSessionZMQ()
modelpath="C:/work/code/modelica/"
Nom_fichier_mo="CyclicLoading.mo"
Nom_fich="CyclicLoading"
fich_res_Modelica_mat="Resultat_av_CyclicLoading.mat"
mod=ModelicaSystem(modelpath+Nom_fichier_mo,Nom_fich,["Modelica","CyclicLoading"])
mod.buildModel()
**mod.setParameters("Nass=12000") **
Directory_cd=omc.sendExpression("cd()")
resultatSimluation=mod.simulate(resultfile=f"{fich_res_Modelica_mat}")
Solution_var=mod.getSolutions()

Trying to change parameters given in open modelica code by changing it with open modelica Python API command. Resulted into error message: | info | setParameters() failed : It is not possible to set the following signal "Nass", It seems to be structural, final, protected or evaluated or has a non-constant binding, use sendExpression(setParameterValue(CyclicLoading, Nass, 12000), parsed=false) and rebuild the model using buildModel() API

Answer 1

There are a number of situations where it is not allowed to change a parameter according to the Modelica specification.

For the following model HelloWorld

model HelloWorld "Model"
  Real x(start=1, fixed = true);
  parameter Real a = 1;       // Changable parameter
  Real y[N];
  parameter Integer N = 2;    // Structural parameter
  final parameter Real b = 3; // Final parameter
protected
  parameter Real c = 4;       // Protected parameter
public
  parameter Real d = 2*a;     // Evaluated parameter

  model M
    parameter Real e = 5;     // Changable parameter
  end M;
  M m(e=d);                   // Non-constant binding of e
equation
  der(x) = a*b*c*d*x;
  for i in 1:N loop
    y[i] = time;
  end for;
end HelloWorld;

it is only allowed to change the value of parameter a.

Without seeing your Modelica model I assume that you encountered one of these cases when trying to change Nass.