dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxxxxxxx>]

Quoting Anders Logg <logg@xxxxxxxxx>:

> On Tue, Aug 23, 2005 at 08:28:32PM +0200, Garth N. Wells wrote:
> > Attached are some patch files which, if they could be added to Dolfin,
> would be
> > really useful for me. They involve:
> > 
> > 1) Time-dependent boundary conditions (BoundaryCondtion.cpp_patch
> > and BoundaryCondtion.h_patch). I've done this in the same way as
> > it's done for a function. It might be nice in the future if the time
> > could be more globally available.
> 
> One possibility would be to add the time as an argument to operator()
> in BoundaryValue:
> 
>     virtual const BoundaryValue operator() (const Point& p, real t);
> 
> but that would require FEM::assemble() to know the time.
> 
> The current implementation (your patch) has the advantage that it
> works in the same way as the Function class. In both cases, a Function
> or a BoundaryValue represents a field on a mesh at a given time
> t. It's not a function of time, but rather a sample at a given time so
> the user needs to explicitly change the time.
> 

A nicer implementaion would be to somehow have the time available for all
objects. The danger now is that time time might be updated for a particular
object and not for another.


> > 2) Computing eigenvalues of a matrix directly using PETSc
> > (GMRES.cpp_patch and GMRES.h_patch). The function replaces the usual
> > "solve". It solves the system and returns n eigenvales in two
> > Vectors - one for the real component and one for the complex
> > component. I haven't added a version for virtual matrices.
> 
> I think this looks a little strange, a function that both solves the
> system and computes eigenvalues. Looks like these two computations are
> carried out independently, so maybe they should be two separate
> functions?

A new class would be nicer. The reason I mades it a PETSc seems to require a
solve before being able to compute the eigenvalues. I'll make a new class that
computes the eigenvalues given a matrix and returns the result in two vectors.
If necessary, I'll just solve a system with a trivial RHS to compute the
eigenvalues. 

> 
> Maybe a new class for computing eigenvalues?
> 
> A related question: should we put some shortcuts for some of the basic
> operations in the dolfin namespace, like
> 
>   dolfin::solve(A, x, b)
>   dolfin::eig(A, l, n)
>   dolfin::assemble(a, A, mesh)
> 
> or should we add easy access as member functions:
> 
>   A.solve(x, b)
>   A.eig(l, n)
> 
> Or both?
> 
> /Anders
> 
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