issue with algebraic loop (nonlinear)

[johhell]

testing a simple control circuit with a nonlinear element and received wrong result.

OM circuit diagram

wrong result - Modia

correct result - Modia

• additional PT1 element used, to open the algebraic loop
• verified with OM simulation (attached)

NoNlinear.zip

idea to avoid incorrect results (can be solved by opening the algebraic loop)

• issue a Warning in module StateSelection function getSortedAndSolvedAST like this

                    if !isLinear
                        @warn "\n===>>> getSortedAndSolvedAST\n===>>> system -$j.$i- NOT linear \n===>>> isLinear: $(isLinear)\n===>>> hasConstCoeff: $(hasConstantCoefficients)\n"
                    end

• reactivate showMessage2 - at the moment commented

                            if linearAssumption
                                isLinear = true
                                hasConstantCoefficients = false
                                #showMessage2("It is heuristically assumed that equation system is linear (although isLinearEquation returned isLinear=false).";
                                #             severity  = WARNING,
                                #             variables = vConstraints[i],
                                #             equations = eConstraints[i])
                            end