dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Oct 31, 2008 at 01:11:48PM +0100, Martin Sandve Alnæs wrote:
> 2008/10/31 Anders Logg <logg@xxxxxxxxx>:
> > On Fri, Oct 31, 2008 at 10:12:03AM +0000, Garth N. Wells wrote:
> >>
> >>
> >> DOLFIN wrote:
> >> > One or more new changesets pushed to the primary dolfin repository.
> >> > A short summary of the last three changesets is included below.
> >> >
> >> > changeset:   5053:a37ad63c855383fa6aae8b15bf20720b1a96398f
> >> > tag:         tip
> >> > user:        Anders Logg <logg@xxxxxxxxx>
> >> > date:        Thu Oct 30 18:53:36 2008 +0100
> >> > files:       demo/pde/poisson/cpp/main.cpp dolfin/fem/DirichletBC.cpp dolfin/function/Constant.cpp dolfin/function/Constant.h dolfin/function/Function.cpp dolfin/function/Function.h
> >> > description:
> >> > Make Constants work (only scalar constructors added so far)
> >> >
> >>
> >> It would make things simple if we stick to scalar constants and I would
> >> be happy with that. Constant vector functions for which all components
> >> are equal are easy too, but not all that useful. Anything else, like a
> >> vector [0, 1] will required a FiniteElement to guarantee the correct
> >> tabulation, right?
> >>
> >> Garth
> >
> > That's not a problem. The FunctionSpace for a Constant will be
> > discovered automatically.
> >
> > If a Constant is used in a Form (a.c = c), then the FunctionSpace will
> > be created automatically.
> >
> > If a Constant is used in a DirichletBC, then the FunctionSpace is
> > known (but will not be assigned to the Constant since it is const).
> >
> 
> If I understand this correctly, this sounds severely limiting and ruins
> the simplicity of "a Function always has a FunctionSpace".

Yes, I agree.

> A Constant should be possible to use everywhere a Function
> is possible to use, including external code.

Yes, this would also be good.

The problem is that if we insist that all Functions always have a
FunctionSpace, then we need to provide a FunctionSpace for Constants.

One option could be to implement/generate a FunctionSpace for
constants and include it in DOLFIN.

-- 
Anders

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