MatCreateSubMatrix#
Gets a single submatrix on the same number of processors as the original matrix.
Synopsis#
#include "petscmat.h"
PetscErrorCode MatCreateSubMatrix(Mat mat, IS isrow, IS iscol, MatReuse cll, Mat *newmat)
Collective
Input Parameters#
mat - the original matrix
isrow - parallel
IS
containing the rows this processor should obtainiscol - parallel
IS
containing all columns you wish to keep. Each process should list the columns that will be in IT’s “diagonal part” in the new matrix.cll - either
MAT_INITIAL_MATRIX
orMAT_REUSE_MATRIX
Output Parameter#
newmat - the new submatrix, of the same type as the original matrix
Notes#
The submatrix will be able to be multiplied with vectors using the same layout as iscol
.
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. For MATBAIJ
and MATSBAIJ
matrices the indices must include all rows/columns of a block;
for example, if the block size is 3 one cannot select the 0 and 2 rows without selecting the 1 row.
The index sets may not have duplicate entries.
The first time this is called you should use a cll of MAT_INITIAL_MATRIX
,
the MatCreateSubMatrix()
routine will create the newmat for you. Any additional calls
to this routine with a mat of the same nonzero structure and with a call of MAT_REUSE_MATRIX
will reuse the matrix generated the first time. You should call MatDestroy()
on newmat
when
you are finished using it.
The communicator of the newly obtained matrix is ALWAYS the same as the communicator of the input matrix.
If iscol
is NULL
then all columns are obtained (not supported in Fortran).
If isrow
and iscol
have a nontrivial block-size, then the resulting matrix has this block-size as well. This feature
is used by PCFIELDSPLIT
to allow easy nesting of its use.
Example usage#
Consider the following 8x8 matrix with 34 non-zero values, that is assembled across 3 processors. Let’s assume that proc0 owns 3 rows, proc1 owns 3 rows, proc2 owns 2 rows. This division can be shown as follows
1 2 0 | 0 3 0 | 0 4
Proc0 0 5 6 | 7 0 0 | 8 0
9 0 10 | 11 0 0 | 12 0
-------------------------------------
13 0 14 | 15 16 17 | 0 0
Proc1 0 18 0 | 19 20 21 | 0 0
0 0 0 | 22 23 0 | 24 0
-------------------------------------
Proc2 25 26 27 | 0 0 28 | 29 0
30 0 0 | 31 32 33 | 0 34
Suppose isrow
= [0 1 | 4 | 6 7] and iscol
= [1 2 | 3 4 5 | 6]. The resulting submatrix is
2 0 | 0 3 0 | 0
Proc0 5 6 | 7 0 0 | 8
-------------------------------
Proc1 18 0 | 19 20 21 | 0
-------------------------------
Proc2 26 27 | 0 0 28 | 29
0 0 | 31 32 33 | 0
See Also#
Matrices, Mat
, MatCreateSubMatrices()
, MatCreateSubMatricesMPI()
, MatCreateSubMatrixVirtual()
, MatSubMatrixVirtualUpdate()
Level#
advanced
Location#
Examples#
src/ksp/ksp/tutorials/ex59.c
src/ksp/ksp/tutorials/ex49.c
src/ksp/ksp/tutorials/ex19.c
src/snes/tutorials/ex73f90t.F90
src/ksp/pc/tutorials/ex4.c
src/ksp/ksp/tutorials/ex64.c
Implementations#
MatCreateSubMatrix_MPIAIJ() in src/mat/impls/aij/mpi/mpiaij.c
MatCreateSubMatrix_SeqAIJ() in src/mat/impls/aij/seq/aij.c
MatCreateSubMatrix_MPIBAIJ() in src/mat/impls/baij/mpi/mpibaij.c
MatCreateSubMatrix_SeqBAIJ() in src/mat/impls/baij/seq/baij2.c
MatCreateSubMatrix_BlockMat() in src/mat/impls/blockmat/seq/blockmat.c
MatCreateSubMatrix_MPIDense() in src/mat/impls/dense/mpi/mpidense.c
MatCreateSubMatrix_SeqDense() in src/mat/impls/dense/seq/dense.c
MatCreateSubMatrix_IS() in src/mat/impls/is/matis.c
MatCreateSubMatrix_KAIJ() in src/mat/impls/kaij/kaij.c
MatCreateSubMatrix_MAIJ() in src/mat/impls/maij/maij.c
MatCreateSubMatrix_Nest() in src/mat/impls/nest/matnest.c
MatCreateSubMatrix_MPISBAIJ() in src/mat/impls/sbaij/mpi/mpisbaij.c
MatCreateSubMatrix_SeqSBAIJ() in src/mat/impls/sbaij/seq/sbaij2.c
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