dolfin team mailing list archive

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

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
> >>
> >> _______________________________________________
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> >
> >
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> >
> 
> 
> 
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-- 
Dr. Garth N. Wells
Faculty of Civil Engineering and Geosciences
Delft University of Technology
Stevinweg 1
2628 CN Delft
The Netherlands

tel.     +31 15 278 7922
fax.     +31 15 278 6383
e-mail   g.n.wells@xxxxxxxxxx
url      http://www.mechanics.citg.tudelft.nl/~garth