Question #133595 on DOLFIN changed: https://answers.launchpad.net/dolfin/+question/133595
Garth Wells proposed the following answer: On 11/11/10 12:45, Thomas Fraunholz wrote: > New question #133595 on DOLFIN: > https://answers.launchpad.net/dolfin/+question/133595 > > I have a time-dependent Cahn-Hilliard-Type problem and I need to > evaluate the angle from the x-axis of a gradient in order to define > my variational problem. The angle of the gradient can be calculated > by using phi = arctan( dc/dy / dc/dx ). This is needed to model an > anisotropic N-fold surface tension with the help of cos(N*phi). > > A very native approach was to use the following lines of code. It > doesn't work of course. But I think it helps to understand my > problem. > > -------------------- import numpy as np from dolfin import * > > ... > > V = FunctionSpace(mesh, "CG", 2) w = TestFunction(V) > > c = Function (V) # current solution c0 = Function(V) # old > solution > > ... > > # Anisotropic N-fold surface tension: def anisotropic_tension(c0): > return np.cos(N*np.arctan2(c0.dx(1),c0.dx(0))) > > L = L - dt*anisotropic_tension(c0)*(inner(div(grad(w)), > div(grad(c)))*dx) > > ... > > -------------------- > > I think one basic problem is the interaction with numpy and the > encapsuled evaluation of the derivatives. I'm glad for any hint how > to proper evaluate the angle and how to use it in order to define L. Try using 'Atan' (a UFL function) directly, e.g. M = dt*N*Atan(....)* . . . . . Garth > You received this question notification because you are a member of DOLFIN Team, which is an answer contact for DOLFIN. _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
