Language Support Status

Rumoca implements a substantial and growing subset of the Modelica language. This page describes what you can rely on today and where the edges are. The ground truth is the continuously-run Modelica Standard Library (MSL) quality gate, which compiles and simulates MSL models on every change and blocks regressions (documented in the Rumoca Internals book).

What Works Well

• Core equation modeling — models, blocks, packages, records, functions, extends, modifications, nested components, connect with potential/flow semantics.
• Continuous dynamics — DAE compilation with structural analysis: matching, sorting (BLT), algebraic-loop tearing, and dummy-derivative index reduction for many higher-index systems.
• Events — when/elsewhen, pre, edge, reinit, sample, if-expressions with event generation, assert, terminate.
• Arrays — declarations, slicing, and the common array builtins, with scalarization where targets require it.
• Initialization — start attributes and initial equation handling.
• Experiment annotations — StopTime, StartTime, Tolerance, Interval, Solver are parsed and used by scenario and browser runs.

Known Limitations

• High-index DAEs: index reduction handles many mechanical-style systems, but some structurally singular formulations (for example the Cartesian pendulum with an explicit length constraint) are still rejected with a structurally singular system diagnostic. Reformulate with generalized coordinates, or watch the release notes — this area is under active development.
• Event-heavy models with implicit solvers: the default (auto) solver currently selects an implicit method that can stall on rapidly switching models. Workaround: --solver rk-like or annotation(experiment(Solver = "rk-like")).
• Arbitrary large libraries: expect better results with explicit examples and pinned packages than with arbitrary unported libraries; the MSL gate tracks exactly which MSL models compile, simulate, and match reference results.
• Direct CLI runs ignore experiment stop time — pass --t-end or use a scenario file ([sim] t_end). Browser/live runs do honor it.

Checking a Specific Model

The fastest way to find out whether your model is supported is to compile it:

rumoca compile MyModel.mo --emit dae-mo

A clean DAE dump means parsing, resolution, type checking, flattening, and DAE lowering all succeeded. Then rumoca sim (or --inspect structure) exercises the structural preparation and the solver. Diagnostics carry source locations and are designed to name the offending equation or variable.

If you hit something the compiler should support, please file an issue with the model at https://github.com/CogniPilot/rumoca/issues.