**-pc_fieldsplit_schur_precondition <self,selfp,user,a11,full> ** -default is a11. See notes for meaning of various arguments

### Notes

If ptype is

a11 then the preconditioner for the Schur complement is generated from the block diagonal part of the preconditioner

matrix associated with the Schur complement (i.e. A11), not the Schur complement matrix

self the preconditioner for the Schur complement is generated from the symbolic representation of the Schur complement matrix:

The only preconditioner that currently works with this symbolic respresentation matrix object is the PCLSC

preconditioner

user then the preconditioner for the Schur complement is generated from the user provided matrix (pre argument

to this function).

selfp then the preconditioning for the Schur complement is generated from an explicitly-assembled approximation Sp = A11 - A10 inv(diag(A00)) A01

This is only a good preconditioner when diag(A00) is a good preconditioner for A00. Optionally, A00 can be

lumped before extracting the diagonal using the additional option -fieldsplit_1_mat_schur_complement_ainv_type lump

full then the preconditioner for the Schur complement is generated from the exact Schur complement matrix representation computed internally by PFIELDSPLIT (this is expensive)

useful mostly as a test that the Schur complement approach can work for your problem

When solving a saddle point problem, where the A11 block is identically zero, using a11 as the ptype only makes sense
with the additional option -fieldsplit_1_pc_type none. Usually for saddle point problems one would use a ptype of self and
-fieldsplit_1_pc_type lsc which uses the least squares commutator to compute a preconditioner for the Schur complement.

### See Also

PCFieldSplitGetSchurPre(), PCFieldSplitGetSubKSP(), PCFIELDSPLIT, PCFieldSplitSetFields(), PCFieldSplitSchurPreType,

MatSchurComplementSetAinvType(), PCLSC

### Level

intermediate

### Location

src/ksp/pc/impls/fieldsplit/fieldsplit.c
### Examples

src/snes/examples/tutorials/ex70.c.html

### Implementations

PCFieldSplitSetSchurPre_FieldSplit in src/ksp/pc/impls/fieldsplit/fieldsplit.c

Index of all PC routines

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Index of all manual pages