Solver Change From Variable to Fixed Step : Transient initialization, solving for consistent states and modes, failed to converge. ...Nonlinear solver: Linear Algebra error. Failed to solve using iteration matrix.

Hello,

When Changed Sovler settings from Variable-step to Fixed-step for Code generation, Follwoing Error reports : Transient initialization, solving for consistent states and modes, failed to converge. Nonlinear solver: Linear Algebra error. Failed to solve using iteration matrix.

Model run fine with Variable-step solver settings. Can you please help me to dianose the issue

Thanks

Arole

[Jim Riggs]

It could be that your model is very stiff and this will cause the fixed-step solver to have trouble.

Note that when using a variable-step solver, it usually includes a high-order solver which has good numerical accuracy. When you switch to fixed-step solver, the only option is Euler, and this has severe limitations in both accuracy and stabilty.

Note that the variable-step solver usually starts with a very small initial step (1e-6, or smaller) and then progressively increases the step size based on the calculated error.

Check the step size that te fixed step solver is using. It will have to be very small (much smaler than the variable-step solver - three orders of magnitude or more). This is a good place to start.

[Sreeraj Arole]

Thank you very much for the insight

Answer 1

[Steve Miller]

When you get this error message during simulation, try

1. Ensure that you are using the local solver (for Simscape models)
2. Making your step size smaller
3. Increasing the number of nonlinear iterations

You should make sure your model runs well during variable-step simulation before attempting to run it with a fixed-step solver.

[Manuel Garcia]

thank for you recommendetion.