On Feb 11, 2008 5:05 AM, Anders Logg <[EMAIL PROTECTED]> wrote: > On Mon, Feb 11, 2008 at 11:54:14AM +0100, Kristen Kaasbjerg wrote: > > Hi dolfin users > > > > I am trying to use dolfin for the following simple > > electrostatic problem: > > - finding the electrostatic potential in a domain composed > > of two subdomains with different dielectric constants. > > This amounts to solving Laplace equation with appropriate > > BC's. > > > > One thing that I cannot figure out how to do is to tell dolfin > > that I have 2 subdomains and on the internal boundary between > > these two domains, the normal derivative of the potential has > > a discontinuity given by the difference between the dielectric > > constants. > > Could anyone give me a hint of how to approach this problem > > with dolfin ? I am relatively unexperienced to FEM so a nice > > reference would also be welcome. > > > > Regards > > Kristen > > The easiest thing to do (if there is just a coefficient in your > problem that is discontinuous) is to just define a Function for the > dielectric constant and make it discontinuous. Then just plug it in to > your equation. > > Look in the demos (under src/demo/pde) for how to define a function. > > For example, if some parameter is 0 or 1 depending on whether x is > below or above 0.5, then just do something like this in eval(): > > if (x[0] > 0.5) > return 1.0; > else > return 0.0;
This is not going to give the correct answer unless you do the boundary integral that comes from the integration by parts. Or am I missing something? Matt > -- > Anders > > _______________________________________________ > DOLFIN-dev mailing list > [email protected] > http://www.fenics.org/mailman/listinfo/dolfin-dev > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener _______________________________________________ DOLFIN-dev mailing list [email protected] http://www.fenics.org/mailman/listinfo/dolfin-dev
