Performance issue: Algebraic loop solution with KINSol

[rruusu]

Description

There are some performance issues when using KINSol for algebraic loops (i.e. the default).

1. The state of the KINSol solver is not mainteined between successive solutions

   • This means that the solver has to start estimating the Jacobian from zero each time

2. The last residual is always evaluated twice in succession

   • Once by KINSol and once by OMSimulator, only for checking the residual value
   • The residual value can be retrieved from KINSol instead.

Expected behavior

Repeated evaluation of the last residual (via calls to fmi2SetReal / fmi2GetReal) is entirely unnecessary.

Solution iterations can be greatly reduced by keeping information from previous solutions.

Version and OS

• Version: OMSimulator v2.1.2.post5-gce342b6-mingw-notlm-debug
• OS: Windows 11, 64-bit

[rruusu]

I will push a solution for this to my fork shortly.

[lochel]

@rruusu Thank you for the feedback! Please feel free to open a pull request with your changes.