dolfin team mailing list archive

[Ola Skavhaug <skavhaug@xxxxxxxxx>]

Anders Logg skrev den 16/12-2007 følgende:
> On Sun, Dec 16, 2007 at 09:46:56AM +0000, Garth N. Wells wrote:
> > 
> > 
> > Gideon Simpson wrote:
> > > I'm interested in implementing the Elman et al. preconditioner for 
> > > Stokes in the fenics suite.  This involves building an approximate schur 
> > > complement for the block strucutre matrix
> > > A B^T
> > > B 0
> > > representing the weak form of the stokes operator.  has anyone 
> > > experimented, if not with this sort, some sort of block structure using 
> > > the fenics front end?
> > > 
> > >
> > 
> > No, when using the default uBLAS backend, there aren't any sophisticated 
> > preconditioners. You can create a preconditioner which derives from 
> > uBLASPreconditioner.
> > 
> > You can also look at using PETSc which provides a variety of 
> > preconditioners.
> > 
> > Garth
> 
> Since this is quite common, maybe we should consider adding a some
> abstractions for block systems/preconditioners: BlockMatrix,
> BlockPreconditioner?
> 
> PyCC has something like this (but only in Python) that we can look at.
> Ola knows more about it.

It would be quite simple to port the block matrices in PyCC to C++. It will
be placed a bit down on my todo list, however.

We have two types of block-matrices:

BlockMatrix
DiagBlockMatrix

Additionally, we have a zero-matrix, since block systems often contain zeros,
and we want to make sure the matrix dimensions in the block system are
correct.

Ola
 
> -- 
> Anders
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