Extract list of variables with start attribute from Modelica model

Question

Is there an easy way to extract a list of all variables with start attribute from a Modelica model? The ultimate goal is to run a simulation until it reaches steady-state, then run a python script that compares the values of start attribute against the steady-state value, so that I can identify start values that were chosen badly.

In the Dymola Python interface I could not find such a functionality. Another approach could be to generate the modelDescription.xml and parse it, I assume the information is available somewhere in there, but for that approach I also feel I need help to get started.

After each simulation, there is a list of iteration variables in the dsin.txt, so it might be easier to extract the information for the txt file. — Jack, Apr 25 '20 at 09:37
related:https://stackoverflow.com/questions/49065763/extract-types-classnames-from-flat-modelica-code, except the method of parsing XML or fmu, there are also some python parsers for Modelica. — Jack, May 07 '20 at 18:45
Use alist.exe to convert dsin.txt and dsfinal.txt to mat files - much easier to load into python, without parsing txt files. — matth, Aug 11 '20 at 07:57

score 3 · Answer 1 · answered Apr 27 '20 at 09:05

The files dsin.txt and dsfinal.txt might help you around with this. They have the same structure, with values at the start and at the end of the simulation; by renaming dsfinal.txt to dsin.txt you can start your simulation from the (e.g. steady-state) values you computed in a previous run.

It might be worthy working with these two files if you have in mind already to use such values for running other simulations.
They give you information about solvers/simulation settings, that you won't find in the .mat result files (if they're of any interest for your case)

However, if it is only a comparison between start and final values of variables that are present in the result files anyway, a better choice might be to use python and a library to read the result.mat file (dymat, modelicares, etc). It is then a matter of comparing start-end values of the signals of interest.

Thanks. Can I somehow filter this to only show variables with start attribute? — Priyanka, Apr 27 '20 at 09:39
Sort of. If you scroll toward the end of a dsin.txt/dsfinal.txt there's a doc explaining the initial values calculation, it seems you can infer which variables have been defined with a start value. But then again, it requires you to parse a txt file, which I understand you prefer not to do — , Apr 27 '20 at 09:57

Priyanka · Answer 2 · 2020-04-28T18:52:23.413

After some trial and error, I came up with this python code snippet to get that information from modelDescription.xml:

import xml.etree.ElementTree as ET
root = ET.parse('modelDescription.xml').getroot()

for ScalarVariable in root.findall('ModelVariables/ScalarVariable'):
    varStart = ScalarVariable.find('*[@start]')
    if varStart is not None:
        name = ScalarVariable.get('name')
        value = varStart.get('start')
        print(f"{name} = {value};")

To generate the modelDescription.xml file, run Dymola translation with the flag
Advanced.FMI.GenerateModelDescriptionInterface2 = true;

Python standard library has several modules for processing XML:
https://docs.python.org/3/library/xml.html
This snippet uses ElementTree.

This is just a first step, not sure if I missed something basic.

score 2 · Accepted Answer · answered Apr 29 '20 at 06:11

Similar to this answer, you can extract that info easily from the modelDescription.xml inside a FMU with FMPy.

Here is a small runnable example:

from fmpy import read_model_description
from fmpy.util import download_test_file
from pprint import pprint

fmu_filename = 'CoupledClutches.fmu'

download_test_file('2.0', 'CoSimulation', 'MapleSim', '2016.2', 'CoupledClutches', fmu_filename)

model_description = read_model_description(fmu_filename)

start_vars = [v for v in model_description.modelVariables if v.start and v.causality == 'local']

pprint(start_vars)

Extract list of variables with start attribute from Modelica model

3 Answers3