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OMJulia.jl

Julia scripting OpenModelica interface.

Overview

OMJulia - the OpenModelica Julia API is a free, open source, highly portable Julia based interactive session handler for Julia scripting of OpenModelica API functionality. It provides the modeler with components for creating a complete Julia-Modelica modeling, compilation and simulation environment based on the latest OpenModelica implementation and Modelica library standard available.

OMJulia is structured to combine both the solving strategy and model building. Thus, domain experts (people writing the models) and computational engineers (people writing the solver code) can work on one unified tool that is industrially viable for optimization of Modelica models, while offering a flexible platform for algorithm development and research. OMJulia is not a standalone package, it depends upon the OpenModelica installation.

OMJulia is implemented in Julia and depends on ZeroMQ - high performance asynchronous messaging library and it supports the Modelica Standard Library version 4.0 that is included with OpenModelica.

Installation

Make sure OpenModelica is installed.

Install OMJulia.jl with:

julia> import Pkg; Pkg.add("OMJulia")

Features of OMJulia

The OMJulia package contains the following features:

  • Interactive session handling, parsing, interpretation of commands and Modelica expressions for evaluation, simulation, plotting, etc.
  • Connect with the OpenModelica compiler through zmq sockets
  • Able to interact with the OpenModelica compiler through the available API
  • Easy access to the Modelica Standard library.
  • All the API calls are communicated with the help of the sendExpression method implemented in a Julia module
  • The results are returned as strings

Tested application areas

OMJulia forwards to omc, which supports the full Modelica language, so nothing here is a language limitation of OMJulia itself. What follows is narrower and more useful: the application areas actually exercised end to end (ModelicaSystem, simulate, linearize, FMU export), so that "it works" means more than "it loaded".

On every pull request, the test suite covers:

  • hybrid, event-driven models — BouncingBall
  • nonlinear DAEs, including the set/get methods, sensitivity analysis and linearization on the same model — a chemical CSTR (ModSeborgCSTRorg)
  • electrical circuits — Modelica.Electrical.Analog.Examples.CauerLowPassAnalog
  • thermal-fluid systems — Modelica.Fluid.Examples.DrumBoiler.DrumBoiler
  • control blocks, and running two sessions at once — Modelica.Blocks.Examples.PID_Controller
  • FMU export through convertMo2Fmu

convertFmu2Mo, the FMU-to-Modelica direction, is not covered: a test for it failed against a real omc in CI (importFMU on a non-trivial FMU, with no diagnostic in getErrorString()) in a way that needs a maintainer with a working omc to debug rather than a guess from here. Treat it as unverified until someone does.

Two broader, non-blocking sweeps run outside the pull-request gate:

  • regression-tests/ simulates, exports an FMU, re-imports it and diffs the result against the direct simulation, for a curated list that adds digital electronics, clocked (sampled-data) systems, and rotational and multibody mechanics. It runs weekly against three omc versions on two operating systems.
  • Every third night, the msl-coverage job asks omc which MSL areas have an Examples package, then simulates every non-partial model under each one's Examples — no curated list, so it tracks whatever MSL version CI has installed. It only checks that the model simulates, not the FMU round trip, and a model failing does not fail the job. The publish-msl-coverage job folds the result into MSL coverage, committed back to the branch that ran it, so the page always reflects the latest sweep rather than whatever was true when this page was last edited by hand.

A model turning up ❌ there does not always mean it is broken. The sweep cannot tell a runnable example from a base class meant to be extended, so some entries under Examples are expected to fail this way; the summary is a starting point for triage, not a verdict.

Other Modelica Standard Library areas that do not have an Examples package — Media, Magnetic, and so on — have been used through OMJulia in practice, but are not exercised by anything above, so they are not claimed here.

What is public

From version 1.0.0 OMJulia follows semantic versioning, so it is worth being explicit about what that covers.

Public, and only broken in a new major version:

Internal, and free to change in any release:

  • OMJulia.Parser and OMJulia.lexer
  • the fields of OMJulia.OMCSession and OMJulia.ZMQSession
  • the element type of the dictionaries the get methods return. They are returned by reference today; treat them as read-only and do not rely on them being Dict{Any, Any}