On Friday 19 March 2010 02:30:40 Anders Logg wrote: > Question #104855 on DOLFIN changed: > https://answers.launchpad.net/dolfin/+question/104855 > > Status: Open => Answered > > Anders Logg proposed the following answer: > When using eval() you need to subclass Expression (not Function). > > That gives you an Expression that can be used in a variational > problem. But an Expression does not have a vector so if you need the > norm of the vector (I guess just for debugging), you need to project > or interpolate the Expression to a Function. > > class Alpha(Expression): > def eval(self, v, x): > v[0] = alpha1 > if x[0] > 0.5: v[0] = alpha2 > > alpha = Alpha() > d = interpolate(alpha, V) > > print " |d| = %g" %(d.vector().norm("l2")) > > -- > Anders > > On Fri, Mar 19, 2010 at 08:49:35AM -0000, Achim Schroll wrote: > > New question #104855 on DOLFIN: > > https://answers.launchpad.net/dolfin/+question/104855 > > > > Hi! > > My piecewise defined function alpha (see below) just returns zero. > > What is wrong? How to define it instead? > > > > Best, Achim > > > > # set parameters > > alpha1 = 0.2; alpha2 = 0.8 > > > > # create mesh and finite element > > mesh = UnitSquare(20, 20) > > V = FunctionSpace(mesh, "CG", 1) > > > > # define trial & testfunctions > > u_trial = TrialFunction(V); phi = TestFunction(V) > > > > # define diffusion parameter > > class alpha(Function): > > def __init__(self, V): > > Function.__init__(self, V) > > def eval(self, v, x): > > v[0] = alpha1 > > if x[0] > 0.5: v[0] = alpha2 > > d = alpha(V) > > print " |d| = %g" %(d.vector().norm("l2"))
What version of DOLFIN are you using. It has not been possible to overload Function.eval in PyDOLFIN since 0.9.5. You might want to upgrade ;) Johan _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
