2007/7/26, Anders Logg <[EMAIL PROTECTED]>:
> Martin Sandve Alnæs wrote:
> > 2007/7/25, Anders Logg <[EMAIL PROTECTED]>:
> >> Martin Sandve Alnæs wrote:
> >> > 2007/7/25, Anders Logg <[EMAIL PROTECTED]>:
> >> >> Martin Sandve Alnæs wrote:
> >> >> > 2007/7/25, Anders Logg <[EMAIL PROTECTED]>:
> >> >> >> 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
>
> I haven't seen this before. Do you mean that the function returning a
> GenericVector will implement the function in GenericTensor returning
> GenericTensor?
Yes. And if you have a GenericTensor* gt, gt->create() will return a
GenericTensor, while a GenericVector* gv; gv->create() returns a
GenericVector. It only works when using subclasses as return types, of
course. So if f.ex. using a smart pointer class, it wouldn't work. You
can even continue:
class MyVec: public GenericVector
{
MyVec * create();
}
This way, we won't have to cast the pointers from create() and copy()
in code that uses f.ex. PetSCVector directly.
> Do you have a reference/link explaining this feature?
It's probably in Bjarne Stroustrups book.
Martin
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