dolfin team mailing list archive

[Vinicius Lobosco <viniciuslobosco@xxxxxxxx>]

I'm new to Fenics, so you should take my comments with lot of criticism. 
Thinking about Pattern Designs, I think that it is best to have only one type 
if classes are nearly the same, what seems to be the case here. Depending of 
the types PDE gets, it should know which specific funcionalities to use. The 
advantage is that PDE users can work with one interface and can use nonlinear 
or linear code at runtime. It will be easier to have an evolving code using 
PDE. I guess that the drawback is that it can get a little slower, but as it 
is not very deep in the iteration structure, I think that it wouldn't be 
noticeable the time difference.

/Vinicius


> Is it preferable to have objects LinearPDE, NonlinearPDE, etc, or just
> one type, PDE, which knows (will be told) whether it is linear,
> nonlinear, time-dependent, etc?
>
> Garth
>
> On Tue, 2006-02-21 at 11:19 +0100, Johan Hoffman wrote:
> > Ok, sounds good. We had a similar structure in early versions of DOLFIN
> > (StatProblem, TranProblem,...), which I think we removed since we wanted
> > a more flat structure of PDE tools. But now we have the possibility to
> > automate a lot of features within each class, so I think a resurrection
> > is motivated.
> >
> > /Johan
> >
> > > I've added the class NonlinearPDE in src/kernel/nls, which has a very
> > > similar interface to the class PDE, and has similar functionality for
> > > solving.
> > >
> > > I think that Anders' suggestion to split-up PDE in the same fashion as
> > > Function is good a good idea. I'm working in it now - at this stage for
> > > linear and nonlinear PDE's.
> > >
> > > Garth
> > >
> > > On Fri, 2006-02-10 at 14:14 -0600, Anders Logg wrote:
> > >> The new PDE class is now in place and takes care of some of the
> > >> standard stuff you need to do to solve a static linear PDE: define
> > >> vectors and matrices, assemble bilinear and linear forms, solve linear
> > >> system and create a Function from the degrees of freedom.
> > >>
> > >> Here's the new version of the Poisson demo:
> > >>
> > >>   // Set up problem
> > >>   UnitSquare mesh(16, 16);
> > >>   Poisson::BilinearForm a;
> > >>   Poisson::LinearForm L(f);
> > >>   PDE pde(a, L, mesh, bc);
> > >>
> > >>   // Solve
> > >>   Function u = pde.solve();
> > >>
> > >>   // Save function to file
> > >>   File file("poisson.pvd");
> > >>   file << u;
> > >>
> > >> This works for all linear static PDEs. I imagine that we can use the
> > >> PDE class to automate the solution of static nonlinear PDEs,
> > >> time-dependent etc. Depending on the arguments to the constructor
> > >> (among other things), the PDE class would know what to do to solve the
> > >> system. A first step would be to integrate Garth's Newton-solver with
> > >> the PDE class. Perhaps we need to partition it in the same way as the
> > >> Function class (GenericPDE, StaticLinearPDE etc) so it's easy to
> > >> plugin a new solver.
> > >>
> > >> Note that as an alternative to
> > >>
> > >>   Function u = pde.solve();
> > >>
> > >> one can do
> > >>
> > >>   Function u;
> > >>   pde.solve(u);
> > >>
> > >> which is slightly more efficient (avoids one copy of the vector of
> > >> degrees of freedom).
> > >>
> > >> The PDE class i parametrized and has one parameter "solver", so you
> > >> can do either
> > >>
> > >>   pde.set("solver", "direct"); // default option
> > >>
> > >> or
> > >>
> > >>   pde.set("solver", "iterative");
> > >>
> > >> /Anders
> > >>
> > >> _______________________________________________
> > >> DOLFIN-dev mailing list
> > >> DOLFIN-dev@xxxxxxxxxx
> > >> http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
> > >
> > > _______________________________________________
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> >
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-- 
-------------------------
Vinicius Lobosco, PhD
Process Intelligence
www.paperplat.com

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