PETSc version 3.16.6

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 irrelevant

- the product matrix

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

For matrix types without special implementation the function fallbacks to MatMatMult() followed by MatTransposeMatMult().

intermediate