petsc-3.9.4 2018-09-11
MatBlockMatSetPreallocation
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 MatBlockMatSetPreallocation(Mat B,PetscInt bs,PetscInt nz,const PetscInt nnz[])
Collective on MPI_Comm
Input Parameters
| B | - The matrix
|
| bs | - size of each block in matrix
|
| nz | - number of nonzeros per block row (same for all rows)
|
| nnz | - array containing the number of nonzeros in the various block rows
(possibly different for each row) or NULL
|
Notes
If nnz is given then nz is ignored
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.
See Also
MatCreate(), MatCreateBlockMat(), MatSetValues()
Level
intermediate
Location
src/mat/impls/blockmat/seq/blockmat.c
Implementations
MatBlockMatSetPreallocation_BlockMat in src/mat/impls/blockmat/seq/blockmat.c
Index of all Mat routines
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Index of all manual pages