libadjoint team mailing list archive

["Marie E. Rognes" <meg@xxxxxxxxx>]

On 06/13/2012 12:29 PM, Patrick Farrell wrote:
> Hi all (Marie in particular!)

Sorry about the near infinite lag here, I just have one further comment
on the PointSource below.

> I want to have a functional J that evaluates the solution u at a certain
> point coords. I know I can do
>
> u(coords)
>
> to evaluate the number, but I was wondering if there's a /symbolic UFL
> expression/ for that operation? Because I want to use it in a
> Functional, so I need to be able to call derivative on it. If I try
>
> derivative(u(coords), u)
>
> it complains of course, because u(coords) is just a float.
>
> I saw your discussion of making a new measure on
> https://bugs.launchpad.net/dolfin/+bug/1010850 --
> I know there's a PointSource class that creates delta functions; but
> how do you actually use it to do an integration?
>
> delta = PointSource(V, Point(0.5))
> inner(u, delta)*dx
>
> fails.

PointSource is a "hack". It is not used as a Function, but as something
you apply to a vector cf:

    
http://fenicsproject.org/documentation/dolfin/1.0.0/cpp/programmers-reference/fem/PointSource.html#pointsource-h

--
Marie

> Am I missing something obvious?
>
> Patrick