On 18 June 2010 17:36, Hans Petter Langtangen <[email protected]> wrote: > Fri, 18 Jun Anders Logg wrote: >> On Fri, Jun 18, 2010 at 04:35:37PM +0200, Hans Petter Langtangen wrote: >> > Fri, 18 Jun Anders Logg wrote: >> > > 3. Is the normal flux + or - grad(u).n? I think of it as -grad(u).n. >> > >> > For k*inner(grad(u), grad(v))*dx, -k*grad(u).n is the right flux. It has >> > a minus sign. Some people use the word flux for grad(u).n, but that's >> > sloppy - normal derivative is then better. >> > >> > Hans Petter >> >> I agree that -k*grad(u).n is the flux, but perhaps the question is >> whether to include the term "flux" at all in the Poisson demo. If it >> is included, then we should have a minus sign, both in the definition >> of g = -k*grad(u).n and in the form where we get -<g, v>*ds. But if we >> don't mention "flux" then it looks strange with two minus signs. > > I agree - in the Poisson demo we skip "flux" and use "normal derivative" > instead and define it as grad(u).n.
OK, I'll change this in the text and code then. Kristian > Hans Petter > > > _______________________________________________ Mailing list: https://launchpad.net/~fenics Post to : [email protected] Unsubscribe : https://launchpad.net/~fenics More help : https://help.launchpad.net/ListHelp
