petsc-3.3-p7 2013-05-11

PCFieldSplitSchurPrecondition

Indicates if the Schur complement is preconditioned by a preconditioner constructed by the A11 matrix. Otherwise no preconditioner is used.

Synopsis

#include "petscpc.h" 
#include "petscdmcomposite.h" 
PetscErrorCode  PCFieldSplitSchurPrecondition(PC pc,PCFieldSplitSchurPreType ptype,Mat pre)

Collective on PC

Input Parameters

	pc	- the preconditioner context
	ptype	- which matrix to use for preconditioning the Schur complement, PC_FIELDSPLIT_SCHUR_PRE_DIAG (diag) is default
	userpre	- matrix to use for preconditioning, or PETSC_NULL

Options Database

-pc_fieldsplit_schur_precondition <self,user,diag> default is diag - Notes:

   If ptype is

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

            to this function).

       diag then the preconditioner for the Schur complement is generated by the block diagonal part of the original

            matrix associated with the Schur complement (i.e. A11)

       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

When solving a saddle point problem, where the A11 block is identically zero, using diag 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 compute a preconditioner for the Schur complement.

Developer Notes: This is a terrible name, gives no good indication of what the function does and should also have Set in the name since it sets a proceedure to use.

PCFieldSplitSchurPrecondition

Synopsis

Input Parameters

Options Database

See Also