schur complement system

[Lisandro Dalcin]

I've just readed Matt mail about an implementation for using schur
complement system.

The actual code is inside petsc4py svn repo at:

http://petsc4py.googlecode.com/svn/trunk/petsc/lib/ext/petsc/src/ksp/pc/impls/

There are a dir named 'schur', that implementation required a global
MATIS. There are another dir named 'schur_aij' wich is an attemp of
implementing the same for global MATMPIAIJ matrices, however this has
not been tested very much.

All this is being using here at CIMEC. I've just posted in petsc-users
a basic description of the (rather involved) implementation.

Take a look in case any of you is insterested. I've never decided to
propose it for inclusion in PETSc because never felt confident all
this really make sense and did not want to contaminate PETSc with a PC
implementation that I do not know will be useful outside our
particular use case.

Regards,

-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
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