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# MatCreateMPIAIJSELL

Creates a sparse parallel matrix whose local portions are stored as SEQAIJSELL matrices (a matrix class that inherits from SEQAIJ but performs some operations in SELL format). The same guidelines that apply to MPIAIJ matrices for preallocating the matrix storage apply here as well.

### Synopsis

```PetscErrorCode  MatCreateMPIAIJSELL(MPI_Comm comm,PetscInt m,PetscInt n,PetscInt M,PetscInt N,PetscInt d_nz,const PetscInt d_nnz[],PetscInt o_nz,const PetscInt o_nnz[],Mat *A)
```
Collective

### Input Parameters

 comm - MPI communicator m - number of local rows (or PETSC_DECIDE to have calculated if M is given) This value should be the same as the local size used in creating the y vector for the matrix-vector product y = Ax. n - This value should be the same as the local size used in creating the x vector for the matrix-vector product y = Ax. (or PETSC_DECIDE to have calculated if N is given) For square matrices n is almost always m. M - number of global rows (or PETSC_DETERMINE to have calculated if m is given) N - number of global columns (or PETSC_DETERMINE to have calculated if n is given) d_nz - number of nonzeros per row in DIAGONAL portion of local submatrix (same value is used for all local rows) d_nnz - array containing the number of nonzeros in the various rows of the DIAGONAL portion of the local submatrix (possibly different for each row) or NULL, if d_nz is used to specify the nonzero structure. The size of this array is equal to the number of local rows, i.e 'm'. For matrices you plan to factor you must leave room for the diagonal entry and put in the entry even if it is zero. o_nz - number of nonzeros per row in the OFF-DIAGONAL portion of local submatrix (same value is used for all local rows). o_nnz - array containing the number of nonzeros in the various rows of the OFF-DIAGONAL portion of the local submatrix (possibly different for each row) or NULL, if o_nz is used to specify the nonzero structure. The size of this array is equal to the number of local rows, i.e 'm'.

### Output Parameter

 A - the matrix

### Notes

If the *_nnz parameter is given then the *_nz parameter is ignored

m,n,M,N parameters specify the size of the matrix, and its partitioning across processors, while d_nz,d_nnz,o_nz,o_nnz parameters specify the approximate storage requirements for this matrix.

If PETSC_DECIDE or PETSC_DETERMINE is used for a particular argument on one processor than it must be used on all processors that share the object for that argument.

The user MUST specify either the local or global matrix dimensions (possibly both).

The parallel matrix is partitioned such that the first m0 rows belong to process 0, the next m1 rows belong to process 1, the next m2 rows belong to process 2 etc.. where m0,m1,m2... are the input parameter 'm'.

The DIAGONAL portion of the local submatrix of a processor can be defined as the submatrix which is obtained by extraction the part corresponding to the rows r1-r2 and columns r1-r2 of the global matrix, where r1 is the first row that belongs to the processor, and r2 is the last row belonging to the this processor. This is a square mxm matrix. The remaining portion of the local submatrix (mxN) constitute the OFF-DIAGONAL portion.

If o_nnz, d_nnz are specified, then o_nz, and d_nz are ignored.

When calling this routine with a single process communicator, a matrix of type SEQAIJSELL is returned. If a matrix of type MPIAIJSELL is desired

### for this type of communicator, use the construction mechanism

MatCreate(...,&A); MatSetType(A,MPIAIJSELL); MatMPIAIJSetPreallocation(A,...);

### Options Database Keys

 -mat_aijsell_eager_shadow - Construct shadow matrix upon matrix assembly; default is to take a "lazy" approach, performing this step the first time the matrix is applied