investigate occasional mumps crashes for large matrices (not reproductible)

DiffractionGratings/grating3D.pro

@@ -500,6 +500,15 @@ PostOperation {
 
 DefineConstant[
   R_ = {"helmholtz_vector", Name "GetDP/1ResolutionChoices", Visible 1},
-  C_ = {"-solve -pos -petsc_prealloc 500 -ksp_type preonly -pc_type lu -pc_factor_mat_solver_type mumps", Name "GetDP/9ComputeCommand", Visible 1},
+  C_ = {"-solve -pos -petsc_prealloc 500 -ksp_type preonly -pc_type lu -pc_factor_mat_solver_type mumps -ksp_error_if_not_converged", Name "GetDP/9ComputeCommand", Visible 1},
   P_ = {"postop_helmholtz_vector", Name "GetDP/2PostOperationChoices", Visible 1}
 ];
+
+// Notes on possible mumps craches (NaN's when large nDOF)
+// -ksp_view
+// -ksp_error_if_not_converged
+// -ksp_monitor_true_residual
+// related to? https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2018-October/036377.html
+
+// N.B. pastix works with petsc 3.12
+// -pc_factor_mat_solver_type pastix
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