petsc3.15.0 20210405
MatCreateSubMatrices
Extracts several submatrices from a matrix. If submat points to an array of valid matrices, they may be reused to store the new submatrices.
Synopsis
#include "petscmat.h"
PetscErrorCode MatCreateSubMatrices(Mat mat,PetscInt n,const IS irow[],const IS icol[],MatReuse scall,Mat *submat[])
Collective on Mat
Input Parameters
 mat   the matrix

 n   the number of submatrixes to be extracted (on this processor, may be zero)

 irow, icol   index sets of rows and columns to extract

 scall   either MAT_INITIAL_MATRIX or MAT_REUSE_MATRIX

Output Parameter
 submat   the array of submatrices

Notes
MatCreateSubMatrices() can extract ONLY sequential submatrices
(from both sequential and parallel matrices). Use MatCreateSubMatrix()
to extract a parallel submatrix.
Some matrix types place restrictions on the row and column
indices, such as that they be sorted or that they be equal to each other.
The index sets may not have duplicate entries.
When extracting submatrices from a parallel matrix, each processor can
form a different submatrix by setting the rows and columns of its
individual index sets according to the local submatrix desired.
When finished using the submatrices, the user should destroy
them with MatDestroySubMatrices().
MAT_REUSE_MATRIX can only be used when the nonzero structure of the
original matrix has not changed from that last call to MatCreateSubMatrices().
This routine creates the matrices in submat; you should NOT create them before
calling it. It also allocates the array of matrix pointers submat.
For BAIJ matrices the index sets must respect the block structure, that is if they
request one row/column in a block, they must request all rows/columns that are in
that block. For example, if the block size is 2 you cannot request just row 0 and
column 0.
Fortran Note
The Fortran interface is slightly different from that given below; it
requires one to pass in as submat a Mat (integer) array of size at least n+1.
See Also
MatDestroySubMatrices(), MatCreateSubMatrix(), MatGetRow(), MatGetDiagonal(), MatReuse
Level
advanced
Location
src/mat/interface/matrix.c
Implementations
MatCreateSubMatrices_MPIAdj in src/mat/impls/adj/mpi/mpiadj.c
MatCreateSubMatrices_MPIAIJ in src/mat/impls/aij/mpi/mpiov.c
MatCreateSubMatrices_SeqAIJ in src/mat/impls/aij/seq/aij.c
MatCreateSubMatrices_MPIBAIJ in src/mat/impls/baij/mpi/baijov.c
MatCreateSubMatrices_SeqBAIJ in src/mat/impls/baij/seq/baij2.c
MatCreateSubMatrices_MPIDense in src/mat/impls/dense/mpi/mmdense.c
MatCreateSubMatrices_SeqDense in src/mat/impls/dense/seq/dense.c
MatCreateSubMatrices_MAIJ in src/mat/impls/maij/maij.c
MatCreateSubMatrices_MPISBAIJ in src/mat/impls/sbaij/mpi/mpisbaij.c
MatCreateSubMatrices_SeqSBAIJ in src/mat/impls/sbaij/seq/sbaij2.c
Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages