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>:
> >> 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.
>
> Yes, A.create() returns a new object that uses the same backend. Since
> the Function class can do things like creating a subfunction and it has
> a copy constructor, it needs to be able to look at a given Function and
> create a new Function which uses the same linear algebra backend. (There
> seems to be a need for this.

Ok.

> Otherwise, we could just let the Function
> class use the default backend.)

No good.

> > 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.
>
> We could have a special factory function for this and it could be named
> copy(). So I suggest one create() and one copy().

Ok.

We can do it like this:

class GenericTensor
{
 GenericTensor * create() = 0;
}

class GenericVector: public GenericTensor
{
 GenericVector * create() = 0;
}

This C++-feature is perhaps not so widely known, but it's useful in
this context.

Martin