PCMGSetGalerkin#

Causes the coarser grid matrices to be computed from the finest grid via the Galerkin process: \(A_{i-1} = r_i * A_i * p_i\).

Synopsis#

#include "petscksp.h" 
PetscErrorCode PCMGSetGalerkin(PC pc, PCMGGalerkinType use)

Logically Collective

Input Parameters#

pc - the multigrid context
use - one of PC_MG_GALERKIN_BOTH, PC_MG_GALERKIN_PMAT, PC_MG_GALERKIN_MAT, or PC_MG_GALERKIN_NONE

Options Database Key#

-pc_mg_galerkin (both|pmat|mat|none) - set the matrices to form via the Galerkin process

Notes#

Some codes that use PCMG such as PCGAMG use Galerkin internally while constructing the hierarchy and thus do not use the PCMG construction of the coarser grids.

If this is not used the coarser grid matrices are computed via re-discretization. That is by calling the function associated with the DM attached to the PC. For example, for nonlinear solves the function provided with SNESSetJacobian().