On Thu, Jun 12, 2008 at 02:42:12PM -0500, Matthew Knepley wrote:
On Thu, Jun 12, 2008 at 2:37 PM, Anders Logg <logg@xxxxxxxxx> wrote:
On Wed, Jun 11, 2008 at 08:11:56AM -0400, mspieg wrote:
Hi all,
is there a simple way to implement a known constant vector
(e.g. the unit
vector jhat = [ 0 1]') into a FFC form?
my specific issue is that the right hand side of my PDE looks like
-\Div f\jhat = - df/dy
where f(x,y) is a user defined scalar function (and df/dy is not
easily
evaluated)
Given a test function v, the weak form (in pseudo-latex) is
\int dv/dy f dx - \int v f \jhat\dot ds
The question is how to evaluate the 2nd term in the FFC form
language (the
volume integral works fine as v.dx(1)*f*dx)
ideally something like
jhat=??
L = v.dx(1)*f*dx) - v*f*jhat*ds
(or more generally for a known unit vector k L=dot(grad(v),k)
*f*dx - v*f*k*ds
)
would be nice (in the same way as simple known constants can be
built in
directly)
But I'm flexible...all help greatly appreciated
marc
It looks like you expect ds to be a vector. It's not. It's a scalar.
But you can get the surface normal as a vector, right? I think that
is what Marc wants.
Matt
Yes, just do
n = FacetNormal(shape)
So I guess what you want to do is
v*f*dot([0, 1], n)*ds
?
--
Anders
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