Enable the usage of a pre-built model executable when instantiating ModelicaSystem

[joewa]

Related Issues

This pull request was inspired from the discussion in issue #151

Purpose

• Enable the usage of a pre-built model executable when instantiating ModelicaSystem. This will gain some efficiency e.g. when only the parameters or the input data changes between different simulation runs.
• Apply the customization (variableFilter or overrides in general) when calling the pre-built model executable (as an alternative to the variableFilter that can be passed to ModelicaSystem or buildModel that was introduced in issue ModelicaSystem.simulate() does not handle 'outputFormat' and 'variableFilter' options correctly. #151).

Approach

ModelicaSystem will not to call buildModel when the xmlFileName of the pre-built model is provided.

from OMPython import ModelicaSystem
mod = ModelicaSystem(
      fileName=`BouncingBall.mo`, modelName='BouncingBall',
      xmlFileName='BouncingBall_init.xml'
  )

The simulation can be executed with a customized set of output variables and stopTime like this:

res_vars = ['h', 'v']
log_str = str(mod.simulate(
    resultfile='/tmp/bouncingball_res.mat',
    simflags=None,
    overrideaux='stopTime={0},'.format(stopTime) + 'variableFilter="'+'|'.join(res_vars)+'"'
))

The log_str contains the models output from stdout and stderr.

Thanks to @Nobby-n and @arun3688 for contribution and inspiration.

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[joewa]

I am happy to provide this PR @arun3688