dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

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.

-- 
Anders