PCGalerkinSetComputeSubmatrix#

Provide a routine that will be called to compute the Galerkin submatrix

Synopsis#

#include "petscksp.h" 
PetscErrorCode PCGalerkinSetComputeSubmatrix(PC pc, PetscErrorCode (*computeAsub)(PC, Mat, Mat, Mat *, void *), void *ctx)

Logically Collective

Input Parameters#

pc - the preconditioner context
computeAsub - routine that computes the submatrix from the global matrix
ctx - context used by the routine, or NULL

Calling sequence of `computeAsub`#

PetscErrorCode computeAsub(PC pc, Mat A, Mat Ap, Mat *cAP, void *ctx);

PC - the PCGALERKIN
A - the matrix in the PCGALERKIN
Ap - the computed submatrix from any previous computation, if NULL it has not previously been computed
cAp - the submatrix computed by this routine
ctx - optional user-defined function context

Notes#

Instead of providing this routine you can call PCGalerkinGetKSP() and then KSPSetOperators() to provide the submatrix, but that will not work for multiple KSPSolve()s with different matrices unless you call it for each solve.

This routine is called each time the outer matrix is changed. In the first call the Ap argument is NULL and the routine should create the matrix and computes its values in cAp. On each subsequent call the routine should up the Ap matrix.

Developer Note#

If the user does not call this routine nor call PCGalerkinGetKSP() and KSPSetOperators() then PCGALERKIN could automatically compute the submatrix via calls to MatGalerkin() or MatRARt()