Symbolic Initialization of Over-determined Higher-index Models
Lennart Ochel, Bernhard Bachmann, Francesco Casella · Linköping electronic conference proceedings · 2014
The quantity of initial equations required in an objectoriented model can only be determined at system level.Since Modelica models are generally designed by components, it is difficult to calculate the amount of initial equations needed at system level, especially when changes are applied to the model, e.g. by adding or removing components.Therefore, it is more convenient to define initial equations at component level.Due to component connections, algebraic dependencies between states may be introduced, which eventually lead to the removal of states when symbolic index reduction algorithms are applied.In this process, the corresponding initial equations are not automatically removed, which results in an over-determined initial system.This paper describes an algorithm that detects such redundant equations and determines if they are consistent or not.Consistent redundant initial equations can thus be removed automatically, and inconsistent ones can be reported to the modeler.A prototype of the algorithm is implemented in OpenModelica, tested on several representative cases, and compared to previously presented concepts.