Conference Contribution

Discontinuities handled with events in Assimulo

Emil Fredriksson, Christian Andersson, Johan Åkesson


Often integrating ordinary differential equations or differential algebraic equations (DAE) do not constitute the problem alone. A common complement is finding the root of an algebraic function (an event function) that depends on the states of the problem. This formulation of a model enables the possibility of including discontinuities, an important part of the Functional Mock-up Interface standard which allows hybrid models of differential algebraic equations. The problem of root-finding during integration is however difficult. Both in a theoretical aspect and as a software problem.

An implementation of software for root-finding is done in Assimulo, a Python/Cython wrapper for integrators. The implementation takes the Functional Mock-up Interface standard into consideration. The implementation is made usable for a wide variety of integration algorithms and is also verified and benchmarked with advanced industrial models, showing good indications of being robust and scaling well for large systems.


Assimulo, FMI, Functional Mock-up Interface, FMU, Discontinuities, Events, Root-finding


In 10th International Modelica Conference, Lund, Sweden, March 2014.

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