Nonlinear solver failed

Hallo Everyone,

can someone please help me? i am trying to solve a LUBBY2 problem but i am getting this error?

Thank you in advance

It is not very much information you provided, but from what I see, it seems that you used very tight convergence criteria. Keep in mind that examples that are more complex than our benchmark examples often also need softer convergence criteria. dx=1e-15 and dx/x=1e-16 sounds very much converged. Please check the criteria (“abstol/reltol”). 4 linear steps are also not many, you can increase the number of nonlinear steps (“max_iter”). And last but not least, you can also tune the time stepping. This error is either due to fixed time stepping or adapted (e.g. iteration_based) time stepping, and the smallest step is reached. Decreasing the step, or the minimal step, of an iteration-based time stepper can also help. But under the given conditions (very small errors and only 4 iterations) I would tune the other parameters first.