dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Monday 22 June 2009 10:51:49 Ola Skavhaug wrote:
> On Mon, Jun 22, 2009 at 10:44 AM, Garth N. Wells<gnw20@xxxxxxxxx> wrote:
> > Johan Hake wrote:
> >> On Saturday 20 June 2009 13:10:46 Garth N. Wells wrote:
> >>> I tried to do
> >>>
> >>>    u0.vector() = u1.vector()
> >>>
> >>> where u0 and u1 are both discrete functions, in PyDOLFIN but it doesn't
> >>> work so I'm using
> >>>
> >>>    u0.vector().assign( u1.vector() )
> >>
> >> This is the correct way to do it. Assignment operators are just ignored
> >> for the dynamically typed languges supported by SWIG. We therefore
> >> rename the foo.operator= to foo.assign.
> >>
> >> However for the Vector and Matrix interfaces we also support the numpy
> >> lookalike assignment:
> >>
> >>   v[:] = u
> >>
> >> and
> >>
> >>   A[:,:] = B
> >>
> >> I have talked to Anders about removing both v.assign and v.set(double *)
> >> and "force" the PyDOLFIN users to use the numpy assignments.
> >
> > Is there any difference in performance between the two?
> >
> > Garth
>
> The slicing means that the actual memory of A is overwritten. I guess
> that is the same as the operator= did before?
> Hence, I guess there will be no big difference.

When I implemented the slicing operator I assumed that the operator= would be 
fastes when a full vector is copied, a la:

  v[:] = u,

because the operator= can use optimized functions from the underlaying la 
library, for example VecCopy for PETSc. So I added a check for this in the 
python slicing operator. If a full slice is assigned, as above, we use the 
assign method, otherwise we use the set(const double*, uint, const uint*) 
method.

Johan

> Ola
>
> >> Johan
> >>
> >>> Is there a fundamental reason why '=' can't be used or does SWIG just
> >>> need to be told how to overload '=' for vectors?
> >>>
> >>> Garth
> >>> _______________________________________________
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> >
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