FMI Layered Standard for DAE (FMI-LS-DAE)

This repository contains an early prototype draft for the FMI Layered Standard for DAE (FMI-LS-DAE) based on the Function Mock-up Interface (FMI).

Based on FMI 3.0, this layered standard plans to define how differential-algebraic equation systems (DAEs) can be exported for ModelExchange.

FMI-LS-DAE Standard

This FMI 3.0 Layered Standard for DAE export is currently maintained in this repository and published at modelica.github.io/fmi-ls-dae/main.

Latest release

Released versions of this layered standard are tagged and listed on the releases page. The specification linked above is built from main and can therefore contain changes that are not part of any release yet.

Reference FMUs

This repository ships its own reference FMUs in reference-FMUs. They are built for all supported platforms by CI and can be downloaded as an artifact:

• SimpleDAE -- a semi-explicit index-1 DAE with two differential states, two algebraic variables, two inputs and two outputs.
• MassSpringOscillator -- an undamped mass-spring oscillator, written as a semi-explicit index-1 DAE with the spring force as the algebraic variable. Its total mechanical energy is exposed as an <Invariant>, which makes it the worked example for invariants and the numerical drift they are meant to detect.

Further FMUs implementing this layered standard are maintained in the modelica/Reference-FMUs repository. Currently there is only one:

• Roberts -- the Robertson problem from chemical kinetics, a semi-explicit index-1 DAE with two differential states and one algebraic variable. It ships the layered standard manifest fmi-ls-dae.xml for FMI-LS-DAE version 1.0.0-alpha.1 and is the worked example of the specification.

Citation

If you use this work, please cite the accompanying pre-print:

Nahodovic et al., "Towards an FMI Layered Standard for DAE: Applications for Simulation and Optimization", arXiv:2606.22544, 2026. https://doi.org/10.48550/arXiv.2606.22544

Copyright and License

Code and documentation copyright (C) 2025 The Modelica Association Project FMI. Code released under the 2-Clause BSD License.

How to Contribute

See CONTRIBUTING.md.

Repository Structure

• docs -- Sources of the specification document
• examples -- Example models and layered standard manifests
• reference-FMUs -- Sources of the reference FMUs of this repository
• schema -- XSD schema for this FMI Layered Standard

Private Sandbox

For development there is a private sandbox modelica/fmi-ls-dae-sandbox to store non-public information.