#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 by the provided matrix (pre argument

to this function).

a11 then the preconditioner for the Schur complement is generated by 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 uses the exact Schur complement (this is expensive)

self the preconditioner for the Schur complement is generated from the Schur complement matrix itself:

The only preconditioner that currently works directly with the Schur complement matrix object is the PCLSC

preconditioner

selfp then the preconditioning matrix is 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; diag is the default.

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