How to multi-grid solver via approximation orders?

[Lukasz Kaczmraczyk]

How to multi-grid solver via approximation orders?

[Lukasz Kaczmraczyk]

Code is run using direct solver, i.e. MUMPS on coarse level. Note that loaded mesh is portioned and each processor only reads part of the mesh, i.e. -my_is_partitioned.

mpirun -np 4 ./elasticity \
 -my_file dam_4parts.h5m -my_is_partitioned \
 -ksp_type gmres -ksp_max_it 1000 -ksp_atol 1e-13 -ksp_rtol 0 -ksp_monitor_lg_residualnorm -ksp_final_residual -ksp_monitor -ksp_converged_reason
 -my_order 1 -my_block_config block_congig.in \
 -mofem_mg_verbose 1 -mofem_mg_coarse_order 1 -mofem_mg_levels 4 \
 -pc_type mg \
 -mg_coarse_ksp_type preonly -mg_coarse_pc_type lu -mg_coarse_pc_factor_mat_solver_package mumps \
 -pc_mg_smoothup 20 -pc_mg_smoothdown 20 -pc_mg_type multiplicative



• Option -my_is_partitioned is set if mesh is partitioned using mbpart
• Option -mofem_mg_coarse_order 1 set coarse level is for linear approximation, i.e. order 1.
• Option -mofem_mg_levels 4 set number of multi-grid level. In that case maximal approx. order for some part of mesh is 4, thus 4 multi-grid levels.
• Option -pc_mg_smoothup 20 -pc_mg_smoothdown 20 set number of smoothing iterations, for more details look to PETSc manual.
• In line
  -mg_coarse_ksp_type preonly -mg_coarse_pc_type lu -mg_coarse_pc_factor_mat_solver_package mumps
  a direct solver for coarse mesh is set.