Hello all,
In my FSI problem, there are 4 vector-valued variables + 3 scalar
variables. Most of them are strongly coupled with each other. It's hard to
decouple the system and design a good preconditoner. Previously, I solved
the whole system with the direct solver (UMFPACK) + Newton's iteration
method.
Several days ago, I added deal.ii's new nonlinear solver (SNES) into my
code, and now its default method is jacobian-free newton-krylov. However,
it behaves bad and never get converged in my case. Maybe I am using it in a
wrong way, as I heard that SNES solver is powerful.
Do you have the experience in using this nonlinear solver? If yes, could
you kindly give me some advice for multiple-variable problem? Do I need to
create block containers for the matrix, solution and right-hand-side ?
Thanks a lot
Lex
constraints_hp.distribute(dis_current_solution);
current_solution = dis_current_solution;
const double target_tolerance = 1.e-8;
PETScWrappers::NonlinearSolverData additional_data;
additional_data.absolute_tolerance = target_tolerance;
additional_data.snes_linesearch_type = "basic";
//additional_data.snes_type = "ngmres" ;
NonlinearSolver nonlinear_solver(additional_data,mpi_communicator);
nonlinear_solver.residual = [&](const VectorType &evaluation_point,
VectorType & residual){
compute_hp_residual(evaluation_point, residual);
};
bool user_control = false;
if (user_control)
{
nonlinear_solver.setup_jacobian =
[&](const VectorType ¤t_u) {
compute_jacobian_and_initialize_preconditioner(current_u);
};
nonlinear_solver.solve_with_jacobian = [&](const VectorType &rhs,
VectorType &dst) {
this->solve(rhs, dst);
};
//nonlinear_solver.set_matrix(jacobian_matrix);
}
else //jacobian-free newton-krylov
{
nonlinear_solver.set_matrix(jacobian_matrix);
nonlinear_solver.jacobian =
[&](const VectorType ¤t_u, MatrixType &, MatrixType &P) {
Assert(P == jacobian_matrix, ExcInternalError());
compute_hp_jacobian_matrix(current_u);
(void)P;
};
}
nonlinear_solver.monitor =
[&](const VectorType &, unsigned int step, double gnorm) {
pcout << step << " norm=" << gnorm << std::endl;
};
nonlinear_solver.solve(dis_current_solution);
constraints_hp.distribute(dis_current_solution);
current_solution = dis_current_solution;
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