Implicit or explicit Simulink solver (stiff or non-stiff systems)

A stiff system is a system having extremely different time scales. Implicit solvers provide greater stability but are computationally more expensive than explicit solvers. This is why a compromise needs to be found. For in-depth information on the dynamic behavior of your model in Simcenter Amesim, use the analysis tools listed in the table below.

Tools to identify the dynamics of the Simcenter Amesim subsystem
	Eigenvalues Use this tool to identify the frequencies and time constants of your system. Use several linearization times if you suspect specific local dynamics of appearing in and disappearing from your model (e.g. opening and closing of a hydraulic valve during the simulation.
	Performance Analyzer Also performs frequency analysis but additionally provides useful statistics on where CPU time is spent. High total number of BDF states could mean that your system is stiff.

The following table indicates when to use an implicit or an explicit Simulink solver:

System	Simulink Solver
Stiff system	Implicit (stable)
Non-stiff system	Explicit (fast)

Note

Most of the classic Simcenter Amesim systems are stiff and require an implicit method to integrate.