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Using Modelica Libraries

Real models build on libraries — most importantly the Modelica Standard Library (MSL). This chapter explains how Rumoca finds library code.

Source Roots

A source root is a file or directory added to the compiler’s search path. When a model references Modelica.Blocks.Continuous.PID, Rumoca resolves the name through the source roots you configured.

On the command line, pass --source-root (repeatable):

rumoca sim my_model.mo \
  --model MyPackage.MyModel \
  --source-root target/msl/ModelicaStandardLibrary-4.1.0/Modelica\ 4.1.0 \
  --source-root helper.mo

In a rum.toml scenario, use the top-level source_roots key with paths relative to the scenario file:

source_roots = ["../modelica_libraries"]

In VS Code, set rumoca.sourceRootPaths (see VS Code Extension).

MODELICAPATH

Rumoca also honors the standard MODELICAPATH environment variable. Entries (:-separated) are appended after explicit --source-root flags, so system-wide library installs resolve without per-command flags.

Pinned Dependencies for the Repository Examples

The examples in the Rumoca repository use pinned library versions declared in examples/modelica_dependencies.toml. Fetch them once:

cargo xtask repo modelica-deps ensure

This downloads MSL and the CogniPilot Modelica Models (CMM) into target/. The repository’s committed VS Code settings reference those directories with workspace-relative paths, so simulation and completion work for every contributor without machine-specific configuration.

Packages and within

Library code is organized as Modelica packages, either as a single .mo file or as a directory tree with package.mo files. The within clause at the top of a library file records which package the file belongs to. When you add a library’s root directory as a source root, all of its classes become resolvable by their fully qualified names.

Practical Tips

  • Prefer pinned library versions over whatever happens to be checked out; scenario files plus pinned paths give reproducible runs.
  • Large library trees compile slower in the browser playground than natively; use the native CLI or VS Code for MSL-heavy work.
  • If a name does not resolve, check Troubleshooting — the usual cause is a missing or wrong source root.