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# MatCheckCompressedRow
Determines whether the compressed row matrix format should be used. Compressed row format provides high performance routines by taking advantage of zero rows. 
## Synopsis
```
#include "petscmat.h"  
PETSC_EXTERN PetscErrorCode MatCheckCompressedRow(Mat A, PetscInt nrows, Mat_CompressedRow *compressedrow, PetscInt *ai, PetscInt mbs, PetscReal ratio)
```
Collective


## Input Parameters

- ***A             -*** the matrix
- ***nrows         -*** number of rows with nonzero entries
- ***compressedrow -*** pointer to the struct Mat_CompressedRow
- ***ai            -*** row pointer used by `MATSEQAIJ` and `MATSEQBAIJ`
- ***mbs           -*** number of (block) rows represented by `ai`
- ***ratio         -*** ratio of (num of zero rows)/m, used to determine if the compressed row format should be used





## Note
Supported types are `MATAIJ`, `MATBAIJ` and `MATSBAIJ`.


## Developer Note
The reason this takes the `compressedrow`, `ai` and `mbs` arguments is because it is called by both the `MATSEQAIJ` and `MATSEQBAIJ` matrices and
the values are not therefore obtained by directly taking the values from the matrix object.
This is not a general public routine and hence is not listed in petscmat.h (it exposes a private data structure) but it is used
by some preconditioners and hence is labeled as `PETSC_EXTERN`


## See Also
 `Mat`, `MATAIJ`, `MATBAIJ`, `MATSBAIJ`.

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/utils/compressedrow.c.html#MatCheckCompressedRow">src/mat/utils/compressedrow.c</A>


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


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