DMSetDefaultConstraints#

Set the PetscSection and Mat that specify the local constraint interpolation.

Synopsis#

#include "petscdm.h"          
#include "petscdmlabel.h"     
#include "petscds.h"     
PetscErrorCode DMSetDefaultConstraints(DM dm, PetscSection section, Mat mat, Vec bias)

Collective

Input Parameters#

  • dm - The DM

  • section - The PetscSection describing the range of the constraint matrix: relates rows of the constraint matrix to dofs of the default section. Must have a local communicator (PETSC_COMM_SELF or derivative).

  • mat - The Mat that interpolates local constraints: its width should be the layout size of the default section: NULL indicates no constraints. Must have a local communicator (PETSC_COMM_SELF or derivative).

  • bias - A bias vector to be added to constrained values in the local vector. NULL indicates no bias. Must have a local communicator (PETSC_COMM_SELF or derivative).

Notes#

If a constraint matrix is specified, then it is applied during DMGlobalToLocalEnd() when mode is INSERT_VALUES, INSERT_BC_VALUES, or INSERT_ALL_VALUES. Without a constraint matrix, the local vector l returned by DMGlobalToLocalEnd() contains values that have been scattered from a global vector without modification; with a constraint matrix A, l is modified by computing c = A * l + bias, l[s[i]] = c[i], where the scatter s is defined by the PetscSection returned by DMGetDefaultConstraints().

If a constraint matrix is specified, then its adjoint is applied during DMLocalToGlobalBegin() when mode is ADD_VALUES, ADD_BC_VALUES, or ADD_ALL_VALUES. Without a constraint matrix, the local vector l is accumulated into a global vector without modification; with a constraint matrix A, l is first modified by computing c[i] = l[s[i]], l[s[i]] = 0, l = l + A’*c, which is the adjoint of the operation described above. Any bias, if specified, is ignored when accumulating.

This increments the references of the PetscSection, Mat, and Vec, so they user can destroy them.

See Also#

DM Basics, DM, DMGetDefaultConstraints()

Level#

advanced

Location#

src/dm/interface/dm.c

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