Thanks for the info. I could probably use piecewise constants for lambda, so that would be fine to have it over each cell.
But I have another another function that will be piecewise linear on the boundary only. And that may be a problem. Let me send the full problem that I want to solve in a separate email. - Shawn On Thu, 16 Apr 2009, [email protected] wrote: > > I would also like this capability! It is something that often shows up > in inverse/optimal control problems. > > Written in FFC/UFL your first equation reads: > > dot(u,v)*dx - p*div(v)*dx + lmbda*dot(v,n)*ds > > where u, p, lmbda are trial functions. > > You could form one system or create a block matrix. Anyhow > the term > lmbda*dot(v,n)*ds > would lead to a matrix with a very big kernel since you are not able to > restrict the dofs of lmbda only to the boundary. > > What you can currently do is to restrict the functionspace for lmbda to > all the cells > associated with the boundary. > > Using restricted functionspaces (in a simpler fashion) can be found in > demo/function/restriction. > > The restriction does only work on cells for now. > > We could discuss Uzawa and/or block matrices for this problem but I think > the simplest start is to create one system to begin with. > > Whether it makes sense that lmbda lives on the whole cell associated with > the boundary, I don't know. > > Kent > > >> On Thu, Apr 16, 2009 at 02:57:07PM -0400, Shawn Walker wrote: >>> Oh really? And then I could call a direct solver on it? Is there a >>> demo >>> somewhere that shows this? >>> >>> I could also use an Uzawa method. But concatenating matrices would be >>> fine for me. >>> >>> - Shawn >> >> No, I don't expect direct solvers will work, but it should be possible >> to use with a Krylov solver. Kent knows about this. >> >> When I look at it now, BlockMatrix does not inherit from any of the >> KrylovMatrix base classes so it won't work with any of the solvers. >> Kent has his own GMRES/CG implementation in Python which uses the >> mult() operator provided by BlockMatrix. Maybe Kent can elaborate on >> this (and the code)? >> >> Moving this to dolfin-dev. >> >> -- >> Anders >> _______________________________________________ >> DOLFIN-dev mailing list >> [email protected] >> http://www.fenics.org/mailman/listinfo/dolfin-dev >> > > > _______________________________________________ > FFC-dev mailing list > [email protected] > http://www.fenics.org/mailman/listinfo/ffc-dev > _______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
