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. Hans Petter _______________________________________________ Mailing list: https://launchpad.net/~fenics Post to : [email protected] Unsubscribe : https://launchpad.net/~fenics More help : https://help.launchpad.net/ListHelp
