dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Aug 17, 2009 at 01:03:55PM +0100, Garth N. Wells wrote:
>
>
> Johan Hake wrote:
> > On Monday 17 August 2009 13:33:21 Garth N. Wells wrote:
> >> Please send any comments on how a SubFunction should work as I'm going
> >> to work on it soon (the Cahn-Hilliard demo runs in parallel(!) ;) with
> >> the exception of the extraction of sub-Functions for output). I'm
> >> inlined to change a sub function such that for
> >>
> >>    Function u0 = u[0]
> >>
> >> the Function u0 will only point the vector belonging to u rather than
> >> creating a new vector. The advantages are:
> >>
> >> - No need to copy a vector
> >> - DofMap will not require 'is_view'
> >> - Possible to do things like
> >>     u0  = 0.0;
> >>     u1  += v;
> >>     u0.interpolate();
> >
> > What would Function::vector() for a SubFunction then return? The original full
> > Vector?
> >
>
> Yes.
>
> > It would be cool to add a view of the original Vector that only represents the
> > values of the dofs in the SubFunction, without coping data. I fiddled around
> > with this when adding slicing for the PyDOLFIN la interface, but realized that
> > it would be too difficult.
> >
>
> This is more or less what I plan to do, although internally. A user
> wouldn't see the vector, but operations like interpolate would only
> involve part of the vector.
>
> We could add a class like
>
>    VectorView(GenericVector& x, DofMap& dof),
>
> which could derive from GenericVector, to provide views. It isn't a
> priority for me though.
>
> Garth

Sounds like this could be coordinated/merged with the functionality
required for the parallel get()/gather(). It's much the same thing,
being able to address a vector with dofs which don't correspond to the
entries in the vector.

--
Anders

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