petsc-3.8.4 2018-03-24

MatMatMatMult

Performs Matrix-Matrix-Matrix Multiplication D=A*B*C.

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

Neighbor-wise Collective on Mat

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

D -the product matrix

Unless scall is MAT_REUSE_MATRIX D will be created.

MAT_REUSE_MATRIX can only be used if the matrices A, B and C 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 use MAT_REUSE_MATRIX in all calls but the first or