dolfin team mailing list archive

["Shilpa Khatri" <khatri@xxxxxxxxxxxx>]

We (Dag and I) are doing this because we would like to have Dolfin solve the
Stokes/Navier-Stokes equations as one part of a timestep in our code where
we are moving interfaces that are defined as a random set of points in the
domain.

Thanks,
Shilpa

On Feb 13, 2008 8:42 PM, Anders Logg <logg@xxxxxxxxx> wrote:

> On Wed, Feb 13, 2008 at 08:28:03PM +0100, Dag Lindbo wrote:
> > > Shilpa Khatri wrote:
> > >> I would also like to know how this is done (We are using the c++
> > >> interface).
> > >> Thanks,
> > >> Shilpa
> > >>
> > >> On Feb 13, 2008 4:09 PM, Kristen Kaasbjerg <cosby@xxxxxxxxx
> > >> <mailto:cosby@xxxxxxxxx>> wrote:
> > >>
> > >>     Hi,
> > >>
> > >>     I have a rather simple question - having obtained a FEM
> > >>     solution "u" of a given PDE, how does one get the
> > >>     function value at an arbitrary point "x" (I'm using the
> > >>     python interface) ?
> > >>
> > >>
> > > This functionality existed in DOLFIN a while ago, but it needs
> updating
> > > to new interfaces. Take a look at the old implementation:
> > >
> > >
> http://www.fenics.org/hg/dolfin?f=50aee5576fed;file=src/kernel/function/DiscreteFunction.cpp
> > >
> > > The point evaluation function is:
> > >
> > > real DiscreteFunction::operator()(const Point& p, uint i)
> > >
> > > The significant change that needs to be done is how to compute basis
> > > functions. This functionality now exists for general finite elements
> in
> > > the UFC interface (evaluate_basis()).
> > >
> > >   Johan
> >
> > This is good news. As far as I can tell, the search is handled by a
> > IntersectionDetector which is mainly a wrapper for GTS. Has the
> _idetector
> > member been removed from the DiscreteFunction, or does it come from some
> > base class?
> >
> > Dag
>
> Why do you need to evaluate functions at arbitrary points?
>
> I can understand it's nice to be able to do this, but in many cases
> there are other solutions (which are much more efficient).
>
> --
> Anders
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-- 
Shilpa M Khatri
Courant Institute of Mathematics - NYU
Royal Institute of Technology (KTH) - Sweden