dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2007/7/25, Anders Logg <logg@xxxxxxxxx>:
> Martin Sandve Alnæs wrote:
> > 2007/7/25, Anders Logg <logg@xxxxxxxxx>:
> >> Garth N. Wells wrote:
> >>> Anders Logg wrote:
> >>>> I think there is a very simple solution. We just change the
> >>>> constructor of Function to
> >>>>
> >>>>     Function(Mesh& mesh, GenericVector& x, const Form& form, uint i = 1)
> >>>>
> >>>> and the vector member of DiscreteFunction to
> >>>>
> >>>>     GenericVector* x;
> >>>>
> >>>> Then if one needs a Function that uses a particular linear algebra
> >>>> backend, then just create the Function from a PETScVector, uBlasVector
> >>>> or EpetraVector. Otherwise, create it from a Vector (tied to the
> >>>> default backend) or let the Function itself decide (in which case it
> >>>> will be a Vector).
> >>>>
> >>> I thought that this would be a simple solution, but there a "new Vector"
> >>> in DiscreteFunction which requires that the vector type be known. If
> >>> this is somehow re-written, the above approach could be used.
> >>>
> >>> Garth
> >> This is used to create copies of the vector (when creating a sub
> >> function or in the copy constructor). How about adding a factory
> >> function to GenericVector? (And also to GenericFoo in general.)
> >>
> >>      virtual GenericVector* create() = 0;
> >>
> >> Then we can call this instead of new Vector() in DiscreteFunction.cpp.
> >>
> >> /Anders
> >
> > I already have this in pycc::GenericVector/Foo, but I call it "copy",
> > which I think is a better name.
>
> I also thought of naming it copy(), but this is not alwats appropriate.
> In DiscreteFunction, one needs to create a new vector which is not a
> copy (but which is a copy of a slice of the vector). Having a copy()
> function might be useful, but one can create a new object and then copy
>    the values by get/set.

So you mean that A.create() returns a non-initialized matrix with
nothing in common with A? I find that a bit confusing, and see no
reason why A should have this ability.

And values aren't the only thing that has to be copied, copy() would
copy or reuse the sparsity pattern and distribution pattern as well.


> > For eventual other situations which require type-independent
> > construction of GenericFoo without an object to copy, we can have a
> > factory design:
> >
> > class GenericFooFactory
> > {
> > public:
> >   GenericFoo * create_foo(...) const = 0;
> >   ...
> > };
> >
> > This is implemented for each backend, and create_foo can be defined
> > with several different argument lists.
> >
> > Martin
>
> Why not place it as a member function in GenericFoo? Then we avoid
> having a number of additional classes (PETScVectorFactor,
> PETScMatrixFactory, uBlasVectorFactory, ...).

Because then you need a GenericFoo object to create a GenericFoo
object, and that's not always the case? It gives me a feeling that the
new returned object has something in common with the object that
created it.

A = dummy_matrix.create()
b = dummy_vector.create()
 vs
A = factory.create_matrix()
b = factory.create_vector()

or
GenericMatrix * matrix()
{
 return factory.create_matrix();
}
A = matrix()


Either dummy_matrix and dummy_vector must be created at some point, or
the factory.

I don't have any very concrete reasons at the moment, it just doesn't
feel right to me. However, looking up on the factory design pattern
might provide some reasons.

Martin