#include "petscpc.h" PetscErrorCode PCFieldSplitSetSchurPre(PC pc,PCFieldSplitSchurPreType ptype,Mat pre)Collective on PC

pc | - the preconditioner context | |

ptype | - which matrix to use for preconditioning the Schur complement: PC_FIELDSPLIT_SCHUR_PRE_A11 (default), PC_FIELDSPLIT_SCHUR_PRE_SELF, PC_FIELDSPLIT_PRE_USER | |

userpre | - matrix to use for preconditioning, or NULL |

If ptype is

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

to this function).

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 he Schur complement matrix

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

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

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: -fieldsplit_1_mat_schur_complement_ainv_type lump

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.

MatSchurComplementSetAinvType(), PCLSC

** Level:intermediate
Location:**src/ksp/pc/impls/fieldsplit/fieldsplit.c

Index of all PC routines

Table of Contents for all manual pages

Index of all manual pages