#include "petscksp.h" PetscErrorCode PCGalerkinSetComputeSubmatrix(PC pc,PetscErrorCode (*computeAsub)(PC,Mat,Mat,Mat*,void*),void *ctx)Logically Collective
| pc | - the preconditioner context | |
| computeAsub | - routine that computes the submatrix from the global matrix | |
| ctx | - context used by the routine, or NULL |
computeAsub(PC pc,Mat A, Mat Ap, Mat *cAP,void *ctx);
| PC | - the Galerkin PC | |
| A | - the matrix in the Galerkin PC | |
| 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 KSPSolves with different matrices unless you call it for each solve.
This routine is called each time the outter 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 Notes: If the user does not call this routine nor call PCGalerkinGetKSP() and KSPSetOperators() then PCGalerkin could could automatically compute the submatrix via calls to MatGalerkin() or MatRARt()