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Rumoca Handbook

Rumoca is a Modelica compiler, simulator, and code generation toolkit written in Rust. It takes equation-based models of physical systems and turns them into simulations you can run from the command line, VS Code, or a browser — or into code for other ecosystems such as Python (SymPy, JAX, CasADi), C, Rust, and FMI.

What is Modelica?

Modelica is an open, equation-based language for modeling physical systems. Instead of writing step-by-step simulation code, you declare the equations that govern your system and let the compiler decide how to solve them.

The example below is a damped spring-mass system. It is live: edit the code, press ▶ Simulate to integrate it right here in your browser, or Show DAE to see the equation system the compiler produces. The editor has the same syntax highlighting, completion, and error checking as the Rumoca VS Code extension, powered by the same compiler running in WebAssembly.

model SpringMassDamper "Mass on a spring with viscous damping"
  parameter Real m = 1.0 "Mass [kg]";
  parameter Real k = 4.0 "Spring constant [N/m]";
  parameter Real c = 0.4 "Damping coefficient [N.s/m]";
  Real x(start = 1.0) "Position [m]";
  Real v(start = 0.0) "Velocity [m/s]";
equation
  der(x) = v;
  m * der(v) = -k * x - c * v;
  annotation(experiment(StopTime = 20.0));
end SpringMassDamper;

Note what you did not have to write: no integration loop, no state vector bookkeeping, no event logic. der(x) means the time derivative of x, and the compiler transforms the equations into a form a numerical solver can integrate.

What Rumoca Gives You

CapabilityWhere to read more
Compile and simulate Modelica modelsQuick Start, Running Simulations
Repeatable scenario files (rum.toml) for simulation and codegenScenario Files
Interactive, human-in-the-loop simulation with browser 3D viewersInteractive Simulation
Code generation to SymPy, JAX, CasADi, C, Rust, FMI, and moreTargets and Templates
IDE support: diagnostics, completion, hover, run buttonsVS Code Extension
Formatter and linter for Modelica sourceFormatter and Linter
Full compiler in WebAssemblyWeb Playground
Structural analysis and debugging of modelsInspecting and Debugging Models

The Normal Workflow

  1. Write or open a Modelica model (.mo file).
  2. Configure any external Modelica package roots, such as the Modelica Standard Library (MSL).
  3. Run a direct command (rumoca sim model.mo) or a colocated rum.toml scenario (rumoca sim -c rum.toml).
  4. Inspect results in the CLI, VS Code, the browser viewer, or generated target output.

Project Status

Rumoca is in active development. It compiles and simulates a growing subset of Modelica, validated continuously against the Modelica Standard Library, but it is not yet a complete replacement for mature tools such as OpenModelica or Dymola. See Language Support Status for an honest description of what works today.

How This Book Is Organized

  • Getting Started installs Rumoca and walks you through your first model.
  • The Modelica Language explains equation-based modeling and what Rumoca supports.
  • Tools covers the CLI, VS Code extension, playground, formatter, and linter.
  • Simulation covers direct runs, scenario files, solvers, interactive simulation, and debugging.
  • Code Generation covers built-in and custom targets.
  • Examples points at runnable examples, including live in-browser ones.

Developers who want to understand or modify the compiler itself should read the companion Rumoca Internals book.