MatCreateShell

Creates a new matrix class for use with a user-defined private data storage format.

Synopsis

#include "petscmat.h" 
int MatCreateShell(MPI_Comm comm,int m,int n,int M,int N,void *ctx,Mat *A)

Collective on MPI_Comm

Input Parameters

	comm	- MPI communicator
	m	- number of local rows (must be given)
	n	- number of local columns (must be given)
	M	- number of global rows (may be PETSC_DETERMINE)
	N	- number of global columns (may be PETSC_DETERMINE)
	ctx	- pointer to data needed by the shell matrix routines

Output Parameter

A -the matrix

Usage

   extern int mult(Mat,Vec,Vec);

   MatCreateShell(comm,m,n,M,N,ctx,&mat);

   MatShellSetOperation(mat,MATOP_MULT,(void(*)(void))mult);

   [ Use matrix for operations that have been set ]

   MatDestroy(mat);

Notes

The shell matrix type is intended to provide a simple class to use with KSP (such as, for use with matrix-free methods). You should not use the shell type if you plan to define a complete matrix class.

PETSc requires that matrices and vectors being used for certain operations are partitioned accordingly. For example, when creating a shell matrix, A, that supports parallel matrix-vector products using MatMult(A,x,y) the user should set the number of local matrix rows to be the number of local elements of the corresponding result vector, y. Note that this is information is required for use of the matrix interface routines, even though the shell matrix may not actually be physically partitioned. For example,

    Vec x, y

    extern int mult(Mat,Vec,Vec);

    Mat A

    VecCreateMPI(comm,PETSC_DECIDE,M,&y);

    VecCreateMPI(comm,PETSC_DECIDE,N,&x);

    VecGetLocalSize(y,&m);

    VecGetLocalSize(x,&n);

    MatCreateShell(comm,m,n,M,N,ctx,&A);

    MatShellSetOperation(mat,MATOP_MULT,(void(*)(void))mult);

    MatMult(A,x,y);

    MatDestroy(A);

    VecDestroy(y); VecDestroy(x);

Keywords

matrix, shell, create

Examples

src/sles/examples/tutorials/ex14f.F.html