MatSeqAIJSetPreallocation#
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 MatSeqAIJSetPreallocation(Mat B, PetscInt nz, const PetscInt nnz[])
Collective
Input Parameters#
B - The matrix
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
Options Database Keys#
-mat_no_inode - Do not use inodes
-mat_inode_limit
- Sets inode limit (max limit=5)
Notes#
If nnz
is given then nz
is ignored
The MATSEQAIJ
format also called
compressed row storage, is fully compatible with standard Fortran
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.
You can call MatGetInfo()
to get information on how effective the preallocation was;
for example the fields mallocs,nz_allocated,nz_used,nz_unneeded;
You can also run with the option -info and look for messages with the string
malloc in them to see if additional memory allocation was needed.
Developer Notes#
Use nz of MAT_SKIP_ALLOCATION
to not allocate any space for the matrix
entries or columns indices
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.
See Also#
Matrices, Mat
, MatCreate()
, MatCreateAIJ()
, MatSetValues()
, MatSeqAIJSetColumnIndices()
, MatCreateSeqAIJWithArrays()
, MatGetInfo()
,
MatSeqAIJSetTotalPreallocation()
Level#
intermediate
Location#
Examples#
src/ksp/ksp/tutorials/ex15f.F90
src/ksp/ksp/tutorials/ex18.c
src/ksp/ksp/tutorials/ex19.c
src/ksp/ksp/tutorials/ex2.c
src/ksp/ksp/tutorials/ex3.c
src/ksp/ksp/tutorials/ex4.c
src/ksp/ksp/tutorials/ex52.c
src/ksp/ksp/tutorials/ex52f.F90
src/ksp/ksp/tutorials/ex54.c
src/ksp/ksp/tutorials/ex55.c
src/ksp/ksp/tutorials/ex56.c
Implementations#
MatSeqAIJSetPreallocation_SeqAIJ in src/mat/impls/aij/seq/aij.c
Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages