# MatShellSetMatProductOperation
Allows user to set a matrix matrix operation for a `MATSHELL` shell matrix. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatShellSetMatProductOperation(Mat A, MatProductType ptype, PetscErrorCode (*symbolic)(Mat, Mat, Mat, void **), PetscErrorCode (*numeric)(Mat, Mat, Mat, void *), PetscErrorCode (*destroy)(void *), MatType Btype, MatType Ctype)
```
Logically Collective on A; No Fortran Support


## Input Parameters

- ***A -*** the `MATSHELL` shell matrix
- ***ptype -*** the product type
- ***symbolic -*** the function for the symbolic phase (can be NULL)
- ***numeric -*** the function for the numerical phase
- ***destroy -*** the function for the destruction of the needed data generated during the symbolic phase (can be NULL)
- ***Btype -*** the matrix type for the matrix to be multiplied against
- ***Ctype -*** the matrix type for the result (can be NULL)





## Usage
```none
      extern PetscErrorCode usersymbolic(Mat,Mat,Mat,void**);
      extern PetscErrorCode usernumeric(Mat,Mat,Mat,void*);
      extern PetscErrorCode userdestroy(void*);
      MatCreateShell(comm,m,n,M,N,ctx,&A);
      MatShellSetMatProductOperation(A,MATPRODUCT_AB,usersymbolic,usernumeric,userdestroy,MATSEQAIJ,MATDENSE);
      [ create B of type SEQAIJ etc..]
      MatProductCreate(A,B,NULL,&C);
      MatProductSetType(C,MATPRODUCT_AB);
      MatProductSetFromOptions(C);
      MatProductSymbolic(C); -> actually runs the user defined symbolic operation
      MatProductNumeric(C); -> actually runs the user defined numeric operation
      [ use C = A*B ]
```



## Notes
`MATPRODUCT_ABC` is not supported yet.

If the symbolic phase is not specified, `MatSetUp()` is called on the result matrix that must have its type set if Ctype is NULL.

Any additional data needed by the matrix product needs to be returned during the symbolic phase and destroyed with the destroy callback.
PETSc will take care of calling the user-defined callbacks.
It is allowed to specify the same callbacks for different Btype matrix types.
The couple (Btype,ptype) uniquely identifies the operation: the last specified callbacks takes precedence.


## See Also
 `MATSHELL`, `MatCreateShell()`, `MatShellGetContext()`, `MatShellGetOperation()`, `MatShellSetContext()`, `MatSetOperation()`, `MatProductType`, `MatType`, `MatSetUp()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/shell/shell.c.html#MatShellSetMatProductOperation">src/mat/impls/shell/shell.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/shell/shell.c.html#MatShellSetMatProductOperation_Shell(Mat A, MatProductType ptype, PetscErrorCode (*symbolic)(Mat, Mat, Mat, void **), PetscErrorCode (*numeric)(Mat, Mat, Mat, void *), PetscErrorCode (*destroy)">MatShellSetMatProductOperation_Shell(Mat A, MatProductType ptype, PetscErrorCode (*symbolic)(Mat, Mat, Mat, void **), PetscErrorCode (*numeric)(Mat, Mat, Mat, void *), PetscErrorCode (*destroy) in src/mat/impls/shell/shell.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/mat/impls/shell/shell.c)


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