dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Feb 25, 2009 at 10:05:34PM +0000, A Navaei wrote:
> I'm not sure if I'm making sense here. Both of you suggested using
> assemble which requires Form which, if I'm not wrong, requires
> Function and that needs FunctionSpace which requires Mesh, but I
> emphasised that this is no FEM problem :) I'm just trying to get the
> best of available LA in dolfin.
> 
> Let me give you a concrete example, have a look at Eq 12 of this paper:
> 
> http://www.mia.uni-saarland.de/Publications/brox-eccv04-of.pdf
> 
> Is it possible to use assemble() to extract A and b out of this
> equation? Many of the coefficients in the equation are image data, I
> guess I should convert the image data to Matrix and use Variable for
> the unknowns?

Yes, this would be fine. You just need to set the values in the matrix
manually using A.set().

But this looks a bit ugly. Why not apply finite elements to solve the
PDE?

-- 
Anders


> -Ali
> 
> 2009/2/25  <kent-and@xxxxxxxxx>:
> >
> > I'm not exactly sure what you are asking. But it is easy to obtain the
> > matrices
> > and vectors in the linear system to be solved.
> >
> > eg.
> > dolfin/demo/la/trilinos/python/demo.py
> >
> > shows how to solve the system using Trilinos. You can use dolfin
> > to make matrices and vectors in PETSc, uBlas, MTL, and Trilinos format.
> > You can choose to let dolfin solve it for you or you can get the underlying
> > matrix and solve it with the above LA libraries.
> >
> > Kent
> >
> >
> >
> >> Is the linear algebra support in dolfin capable of automatically
> >> generating the sparse linear system of equations? (I know that ffc
> >> effectively does this, but note that this question does not involve
> >> solving a PDE using FEM, but a linear system of equations).
> >>
> >> For example, assume we have some busy sets of linear equations and we
> >> wish to convert them to Ax = b so that we can feed them to the linear
> >> solvers. Is there any way of automatically obtaining A and b avoiding
> >> manual calculations and hard-coding?
> >>
> >>
> >> -Ali
> >> _______________________________________________
> >> DOLFIN-dev mailing list
> >> DOLFIN-dev@xxxxxxxxxx
> >> http://www.fenics.org/mailman/listinfo/dolfin-dev
> >>
> >
> >
> >
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@xxxxxxxxxx
> http://www.fenics.org/mailman/listinfo/dolfin-dev

Attachment: signature.asc
Description: Digital signature