dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Wednesday February 16 2011 09:07:57 Garth N. Wells wrote:
> On 16/02/11 16:54, Johan Hake wrote:
> > Question #145534 on DOLFIN changed:
> > https://answers.launchpad.net/dolfin/+question/145534
> > 
> > Johan Hake proposed the following answer:
> > 
> > On Wednesday February 16 2011 08:48:38 Anders Logg wrote:
> >> Question #145534 on DOLFIN changed:
> >> https://answers.launchpad.net/dolfin/+question/145534
> >> 
> >>     Status: Open => Answered
> >> 
> >> Anders Logg proposed the following answer:
> >> 
> >> On Tue, Feb 15, 2011 at 10:30:06PM -0000, Yi Jiang wrote:
> >>> New question #145534 on DOLFIN:
> >>> https://answers.launchpad.net/dolfin/+question/145534
> >>> 
> >>> Hi all,
> >>> 
> >>> I am using the dolfin to solve a PDE problem by finite element method.
> >>> However, I met a problem when I try to define the linear form L(v) of
> >>> right hand side. Suppose the PDE is:
> >>> 
> >>> F(x) = f.
> >>> 
> >>> What should I do if the f is a Dirac Delta function. How to define it
> >>> in ufl? Anybody met and solved the similar problems before?
> >>> Thank you for attention and kind help.
> >> 
> >> This is not supported.
> > 
> > I am also interested in this. What would it require to implement? Changes
> > to UFL, FFC, DOLFIN?
> 
> A lot of changes. It would require being able to integrate over
> surfaces/lines within a cell.
> 
> UFL can be stretched to do this, but extentions to FFC and DOLFIN are
> needed. Take a look at the modelling discontinuities chapter in the
> FEniCS book ;).

Looking forward to do that! 

A naive thought would be to introduce a DeltaDiracFunction which evaluates to 
zero for all but a given coordinates which need to coincide with a vertex. But 
I guess we need to prevent DOLFIN to interpolate the function during assemble, 
and just evaluate it at the quadrature points, where it evaluates to zero?

Johan

> Garth
> 
> > Johan
> 
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