petsc-3.6.2 2015-10-02
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# DMSetDefaultConstraints

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

### Synopsis

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

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, l[s[i]] = c[i], where the scatter s is defined by the PetscSection returned by DMGetDefaultConstraintMatrix().

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.

collective on dm

### 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).

Note: This increments the references of the PetscSection and the Mat, so they user can destroy them

### See Also

DMGetDefaultConstraints()

Level:advanced
Location: src/dm/interface/dm.c
Index of all DM routines
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Index of all manual pages