petsc-3.13.6 2020-09-29

DMCreateMatrix

Gets empty Jacobian for a DM

Synopsis

#include "petscdm.h"          
#include "petscdmlabel.h"     
#include "petscds.h"     
PetscErrorCode  DMCreateMatrix(DM dm,Mat *mat)

Collective on dm

Input Parameter

dm -the DM object

Output Parameter

mat -the empty Jacobian

Notes

This properly preallocates the number of nonzeros in the sparse matrix so you do not need to do it yourself.

By default it also sets the nonzero structure and puts in the zero entries. To prevent setting the nonzero pattern call DMSetMatrixPreallocateOnly()

For structured grid problems, when you call MatView() on this matrix it is displayed using the global natural ordering, NOT in the ordering used internally by PETSc.

For structured grid problems, in general it is easiest to use MatSetValuesStencil() or MatSetValuesLocal() to put values into the matrix because MatSetValues() requires the indices for the global numbering for DMDAs which is complicated.

Level

beginner

Location

src/dm/interface/dm.c

Examples

src/ksp/ksp/tutorials/ex42.c.html
src/ksp/ksp/tutorials/ex43.c.html
src/ksp/ksp/tutorials/ex46.c.html
src/ksp/ksp/tutorials/ex49.c.html
src/ksp/ksp/tutorials/ex65.c.html
src/ksp/ksp/tutorials/ex67.c.html
src/ksp/ksp/tutorials/ex69.c.html
src/ksp/ksp/tutorials/ex70.c.html
src/ksp/ksp/tutorials/ex71.c.html
src/ksp/ksp/tutorials/ex73.c.html
src/ksp/ksp/tutorials/ex44f.F90.html

Implementations