Merge pull request #4339 from GiudGiud/PR_abs_step

Add warning on using the absolute step tolerance with a PETSc nonlinear solver

Author: roystgnr

src/solvers/petsc_nonlinear_solver.C

@@ -970,6 +970,10 @@ PetscNonlinearSolver<T>::solve (SparseMatrix<T> &  pre_in,  // System Preconditi
                                      this->max_nonlinear_iterations,
                                      this->max_function_evaluations));
 
+  // Not supported by PETSc
+  if (this->absolute_step_tolerance != 0) // 0 is default value, both in MOOSE and libMesh
+    libmesh_warning("Setting the absolute step tolerance is not supported with the PETSc nonlinear solver.");
+
   // Set the divergence tolerance for the non-linear solver
 #if !PETSC_VERSION_LESS_THAN(3,8,0)
   LibmeshPetscCall(SNESSetDivergenceTolerance(_snes, this->divergence_tolerance));

src/solvers/trilinos_nox_nonlinear_solver.C

@@ -385,6 +385,9 @@ NoxNonlinearSolver<T>::solve (SparseMatrix<T> &  /* jac_in */,  // System Jacobi
   Teuchos::RCP<NOX::Epetra::Group> grpPtr = Teuchos::rcp(new NOX::Epetra::Group(printParams, iReq, x, linSys));
   NOX::Epetra::Group & grp = *(grpPtr.get());
 
+  if (this->relative_step_tolerance != 0) // 0 is default value
+    libmesh_warning("Setting the relative step tolerance is currently not supported with the trilinos nox nonlinear solver.");
+
   Teuchos::RCP<NOX::StatusTest::NormF> absresid =
     Teuchos::rcp(new NOX::StatusTest::NormF(this->absolute_residual_tolerance, NOX::StatusTest::NormF::Unscaled));
   Teuchos::RCP<NOX::StatusTest::NormF> relresid =