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# MatShellGetOperation

Gets a matrix function for a `MATSHELL` shell matrix.

## Synopsis

    #include "petscmat.h"
    PetscErrorCode MatShellGetOperation(Mat mat, MatOperation op, PetscErrorCodeFn **g)

Not Collective

## Input Parameters

- mat - the `MATSHELL` shell matrix

- op - the name of the operation

## Output Parameter

- g - the function that provides the operation.

## Notes

See the file include/petscmat.h for a complete list of matrix operations, which all have the form MATOP_, where is the name (in all capital letters) of the user interface routine (e.g., `MatMult()` -> `MATOP_MULT`).

All user-provided functions have the same calling sequence as the usual matrix interface routines, since they are intended to be accessed via the usual matrix interface routines, e.g.,

      MatMult(Mat, Vec, Vec) -> usermult(Mat, Vec, Vec)

Within each user-defined routine, the user should call `MatShellGetContext()` to obtain the user-defined context that was set by `MatCreateShell()`.

## See Also

Matrices, `Mat`, `MATSHELL`, `MatCreateShell()`, `MatShellGetContext()`, `MatShellSetOperation()`, `MatShellSetContext()`

## Level

advanced

## Location

src/mat/impls/shell/shell.c

## Implementations

MatShellGetOperation_Shell() in src/mat/impls/shell/shell.c

Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages