dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Tue, Jul 12, 2005 at 06:49:40PM +0200, Garth N. Wells wrote:
> Attached are files for SUPG stabilised convection-diffusion. They
> simply replace existing files in src/modules/convdiff and
> src/modules/convdiff/dolfin.

Great! I've been waiting for someone to come along and stabilize the
convection-diffusion module.

I'll add this, but probably not today (and perhaps not until after my
vacation).

> The stabilisation terms are computed in a very simple
> fashion. Things could be made simpler if it were possible to perform
> more algebraic operations on functions with ffc such as taking
> square roots, inverses, etc. Would this be possible Anders?

Yes, I think it's possible to extend the capabilities of FFC to handle
almost any kind of operations applied to Function (but not to
BasisFunction). This can be done by replacing each operation

    op

with

    pi op pi

where pi is a projection or interpolant onto the finite element space.

In the simplest case, pi is just nodal interpolation and op is defined
point-wise, so if w is a given function, then

    op w --> pi op pi w = pi op sum_i w_i phi_i
                        = sum_i op(w_i) phi_i

In the case of the square-root, we would just take the square-roots of
the expansion coefficients and this might as well be done by FFC as by
DOLFIN. (FFC would generate a couple of extra lines of code for doing
the operations on the expansion coefficients.)

I'll add this to my TODO list.

/Anders