# MatCreateSeqAIJ#

Creates a sparse matrix in MATSEQAIJ (compressed row) format (the default parallel PETSc format). For good matrix assembly performance the user should preallocate the matrix storage by setting the parameter nz (or the array nnz). By setting these parameters accurately, performance during matrix assembly can be increased by more than a factor of 50.

## Synopsis#

#include "petscmat.h"
PetscErrorCode MatCreateSeqAIJ(MPI_Comm comm, PetscInt m, PetscInt n, PetscInt nz, const PetscInt nnz[], Mat *A)


Collective

## Input Parameters#

• comm - MPI communicator, set to PETSC_COMM_SELF

• m - number of rows

• n - number of columns

• nz - number of nonzeros per row (same for all rows)

• nnz - array containing the number of nonzeros in the various rows (possibly different for each row) or NULL

## Output Parameter#

• A - the matrix

It is recommended that one use the MatCreate(), MatSetType() and/or MatSetFromOptions(), MatXXXXSetPreallocation() paradigm instead of this routine directly. [MatXXXXSetPreallocation() is, for example, MatSeqAIJSetPreallocation()]

## Notes#

If nnz is given then nz is ignored

The AIJ format, also called compressed row storage, is fully compatible with standard Fortran 77 storage. That is, the stored row and column indices can begin at either one (as in Fortran) or zero. See the users’ manual for details.

Specify the preallocated storage with either nz or nnz (not both). Set nz = PETSC_DEFAULT and nnz = NULL for PETSc to control dynamic memory allocation. For large problems you MUST preallocate memory or you will get TERRIBLE performance, see the users’ manual chapter on matrices.

By default, this format uses inodes (identical nodes) when possible, to improve numerical efficiency of matrix-vector products and solves. We search for consecutive rows with the same nonzero structure, thereby reusing matrix information to achieve increased efficiency.

## Options Database Keys#

• -mat_no_inode - Do not use inodes

• -mat_inode_limit - Sets inode limit (max limit=5)

Sparse Matrix Creation, MatCreate(), MatCreateAIJ(), MatSetValues(), MatSeqAIJSetColumnIndices(), MatCreateSeqAIJWithArrays()

intermediate

## Location#

src/mat/impls/aij/seq/aij.c

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