petsc-3.7.5 2017-01-01
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MatSchurComplementGetPmat

 Obtain a preconditioning matrix for the Schur complement by assembling Sp = A11 - A10 inv(diag(A00)) A01

Synopsis

#include "petscksp.h" 
PetscErrorCode  MatSchurComplementGetPmat(Mat S,MatReuse preuse,Mat *Sp)
Collective on Mat

Input Parameters

S - matrix obtained with MatCreateSchurComplement() (or equivalent) and implementing the action of A11 - A10 ksp(A00,Ap00) A01
preuse - MAT_INITIAL_MATRIX for a new Sp, or MAT_REUSE_MATRIX to reuse an existing Sp, or MAT_IGNORE_MATRIX to put nothing in Sp

Output Parameter

Sp -approximate Schur complement suitable for preconditioning S = A11 - A10 inv(diag(A00)) A01

Note

Since the real Schur complement is usually dense, providing a good approximation to newpmat usually requires application-specific information. The default for assembled matrices is to use the inverse of the diagonal of the (0,0) block A00 in place of A00^{-1}. This rarely produce a scalable algorithm. Optionally, A00 can be lumped before forming inv(diag(A00)).

Sometimes users would like to provide problem-specific data in the Schur complement, usually only for special row and column index sets. In that case, the user should call PetscObjectComposeFunction() to set "MatSchurComplementGetPmat_C" to their function. If their function needs to fall back to the default implementation, it should call MatSchurComplementGetPmat_Basic().

See Also

MatGetSubMatrix(), PCFIELDSPLIT, MatGetSchurComplement(), MatCreateSchurComplement(), MatSchurComplementSetAinvType()

Level:advanced
Location:src/ksp/ksp/utils/schurm.c
Index of all KSP routines
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Index of all manual pages