dolfin team mailing list archive

[Ola Skavhaug <skavhaug@xxxxxxxxx>]

Anders Logg skrev den 31/03-2008 følgende:
> On Mon, Mar 31, 2008 at 01:11:42PM +0200, Martin Sandve Alnæs wrote:
> > 2008/3/31, Anders Logg <logg@xxxxxxxxx>:
> > > On Sun, Mar 30, 2008 at 11:04:57PM +0200, Martin Sandve Alnæs wrote:
> > >  > 2008/3/30, Anders Logg <logg@xxxxxxxxx>:
> > >  > > On Sun, Mar 30, 2008 at 10:25:06PM +0200, Martin Sandve Alnæs wrote:
> > >  > >  > Then solve should be fixed to expect a GenericVector, what's the problem?
> > >  > >
> > >  > >
> > >  > > Yes, but that needs some thinking. The solve() function needs to check
> > >  > >  what kind of arguments it gets and redirect to the correct backend.
> > >  > >  For example, if (A, x, b) are PETSc objects, then it needs to call a
> > >  > >  PETSc solver (which does not work through the GenericFoo interface).
> > >  > >
> > >  > >  I guess you can work your magic try { dynamic_cast<...> } here?
> > >  >
> > >  > Sure, that should be easy. I'll look at it tomorrow.
> > >
> > >
> > > Fint!
> > >
> > >  solve() ligger i dolfin/la/solve.{h,cpp}
> > 
> > Vector creates problems when testing the type of a GenericVector.
> > 
> > All code that wants to test the type of a GenericVector
> > will depend on Vector.
> > 
> > Do you really want all this type trouble just to be able to write
> > 
> >   Vector v;
> > 
> > instead of
> > 
> >   typedef FooVec Vector;
> >   ...
> >   GenericVector *v = new Vector()
> 
> Yes! "Vector v" looks almost infinitely better than having to write
> typedefs and calling new.
> 
> But we don't really need to fix solve() if it's too much trouble.
> If we don't want to dynamically resolve the representation of matrices
> and vectors, then there will be some functions such as assemble() that
> work for any type of vector (GenericVector) and there will be others
> that work only for a specific implementation.
> 
> So, if you have a Vector, then you can use it with everything:
> 
>    assemble()
>    solve()
>    LUSolver
>    KrylovSolver
> 
> but if you have a FooVector, then you must use it with the
> Foo solvers:
> 
>    FooLUSolver
>    FooKrylovSolver
> 
> So, if it's too much trouble to resolve the backend dynamically, then
> we don't really need to do it.
> 
> The basic idea here is that if you don't care about the backend,
> just use Matrix and Vector and everything is simple (assemble, solve).
> 
> But if you want to use some special backend, then use FooMatrix,
> FooVector and FooSolver.

That is the problem in having a simpler design, omitting the Matrix-wrapper
construction, and using only a typedef? F.ex.

typedef Matrix uBlasMatrix;

If we are consistent in the DOLFIN library, only communicating GenericFoo
across the interfaces, the chances of non-compatible code being propagated
into the library is minimal. The only place the additional methods of a
particular backend can be used is in user space (and hence not our
concern).

This will give the nice syntax Anders wants, and conforms with standard
oo-design. The cost is that methods added to a backend will be accessible
through the Matrix typedef, and this might lead to non-portable _user_ code.

??

Ola


 
> -- 
> Anders
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