petsc-3.3-p7 2013-05-11

MatMatMult

Performs Matrix-Matrix Multiplication C=A*B.

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

Neighbor-wise Collective on Mat

	A	- the left matrix
	B	- the right matrix
	scall	- either MAT_INITIAL_MATRIX or MAT_REUSE_MATRIX
	fill	- expected fill as ratio of nnz(C)/(nnz(A) + nnz(B)), 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

Unless scall is MAT_REUSE_MATRIX C will be created.

MAT_REUSE_MATRIX can only be used if the matrices A and B have the same nonzero pattern as in the previous call

To determine the correct fill value, run with -info and search for the string "Fill ratio" to see the value actually needed.

If you have many matrices with the same non-zero structure to multiply, you should either

  1) use MAT_REUSE_MATRIX in all calls but the first or

  2) call MatMatMultSymbolic() once and then MatMatMultNumeric() for each product needed