petsc-3.7.3 2016-07-24
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# MatSchurComplementGetAinvType

get the type of approximation for the inverse of the (0,0) block used in forming Sp in MatSchurComplementGetPmat()

### Synopsis

    #include "petscksp.h"
    PetscErrorCode  MatSchurComplementGetAinvType(Mat S,MatSchurComplementAinvType *ainvtype)

Not collective.

### Input Parameter

S -matrix obtained with MatCreateSchurComplement() (or equivalent) and implementing the action of A11 - A10 ksp(A00,Ap00) A01

### Output Parameter

ainvtype -type of approximation used to form A00inv from A00 when assembling Sp = A11 - A10 A00inv A01: MAT_SCHUR_COMPLEMENT_AINV_DIAG or MAT_SCHUR_COMPLEMENT_AINV_LUMP

### 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)).

### See Also

MatSchurComplementAinvType, MatCreateSchurComplement(), MatGetSchurComplement(), MatSchurComplementGetPmat(), MatSchurComplementSetAinvType()

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