petsc-3.7.7 2017-09-25

MatPtAP

Creates the matrix product C = P^T * A * P

#include "petscmat.h" 
PetscErrorCode MatPtAP(Mat A,Mat P,MatReuse scall,PetscReal fill,Mat *C)

Neighbor-wise Collective on Mat

	A	- the matrix
	P	- the projection matrix
	scall	- either MAT_INITIAL_MATRIX or MAT_REUSE_MATRIX
	fill	- expected fill as ratio of nnz(C)/(nnz(A) + nnz(P)), use PETSC_DEFAULT if you do not have a good estimate if the result is a dense matrix this is irrelevent

C -the product matrix

C will be created and must be destroyed by the user with MatDestroy().

This routine is currently only implemented for pairs of AIJ matrices and classes which inherit from AIJ.