# MatCheckCompressedRow
Determines whether the compressed row matrix format should be used. If the format is to be used, this routine creates Mat_CompressedRow struct. Compressed row format provides high performance routines by taking advantage of zero rows. Supported types are MATAIJ, MATBAIJ and MATSBAIJ. 
## 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 seqaij and seqbaij
- ***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


Developer Note: The reason this takes the compressedrow, ai and mbs arguments is because it is called by both the SeqAIJ and SEQBAIJ 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



## 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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