petsc-3.12.5 2020-03-29

MatMatMult

Performs Matrix-Matrix Multiplication C=A*B.

Synopsis

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

Neighbor-wise Collective on Mat

Input Parameters

	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

Output Parameters

C -the product matrix

Notes

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 and C was obtained from a previous call to this function with either MAT_INITIAL_MATRIX or MatMatMultSymbolic()

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

In the special case where matrix B (and hence C) are dense you can create the correctly sized matrix C yourself and then call this routine with MAT_REUSE_MATRIX, rather than first having MatMatMult() create it for you. You can NEVER do this if the matrix C is sparse.

Level

intermediate

Location

src/mat/interface/matrix.c

Examples

src/snes/examples/tutorials/ex70.c.html

Implementations