:orphan:
# MatSetValuesIS
Inserts or adds a block of values into a matrix using an `IS` to indicate the rows and columns These values may be cached, so `MatAssemblyBegin()` and `MatAssemblyEnd()` MUST be called after all calls to `MatSetValues()` have been completed. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatSetValuesIS(Mat mat, IS ism, IS isn, const PetscScalar v[], InsertMode addv)
```
Not Collective


## Input Parameters

- ***mat -*** the matrix
- ***v -*** a logically two-dimensional array of values
- ***ism -*** the rows to provide
- ***isn -*** the columns to provide
- ***addv -*** either `ADD_VALUES` to add values to any existing entries, or `INSERT_VALUES` to replace existing entries with new values





## Notes
By default the values, `v`, are stored row-oriented. See `MatSetOption()` for other options.

Calls to `MatSetValues()` with the `INSERT_VALUES` and `ADD_VALUES`
options cannot be mixed without intervening calls to the assembly
routines.

`MatSetValues()` uses 0-based row and column numbers in Fortran
as well as in C.

Negative indices may be passed in `ism` and `isn`, these rows and columns are
simply ignored. This allows easily inserting element stiffness matrices
with homogeneous Dirchlet boundary conditions that you don't want represented
in the matrix.


## Efficiency Alert
The routine `MatSetValuesBlocked()` may offer much better efficiency
for users of block sparse formats (`MATSEQBAIJ` and `MATMPIBAIJ`).

This is currently not optimized for any particular `ISType`


## Developer Notes
This is labeled with C so does not automatically generate Fortran stubs and interfaces
because it requires multiple Fortran interfaces depending on which arguments are scalar or arrays.


## See Also
 [](ch_matrices), `Mat`, `MatSetOption()`, `MatSetValues()`, `MatAssemblyBegin()`, `MatAssemblyEnd()`, `MatSetValuesBlocked()`, `MatSetValuesLocal()`,
`InsertMode`, `INSERT_VALUES`, `ADD_VALUES`, `MatSetValues()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/interface/matrix.c.html#MatSetValuesIS">src/mat/interface/matrix.c</A>


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


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