Evaluation of Gradients/Fluxes at the boundaries

[Burak Atakan]

Thanks for the last answer. I've a new question:


For a 2D-diffusion problem, I would like to fix the concentration (to zero) for
parts of the bottom (from 0 to 'Ende'), 
while the flux should be zero for the rest.
For the part where the concentration is fixed I would like to evaluate the
gradient, finally to get the (species)flux at these positions.


I tried the following:
###################################
BCs = (FixedValue(faces=mesh.getFacesBottom()[0:Ende],
                  value=bot))
       ...
for step in range(steps):
    eq.solve(var=phi,
             boundaryConditions=BCs,
             dt=timeStepDuration)
idsBottom=mesh.getFacesBottom().ids

fl=phi.getFaceGrad()[idsBottom,0]
###################################
However, the fluxes at locations > Ende do not vanish as I expected.

Is there an easier way of getting the gradients or fluxes at the 
boundaries, or
am I doing something wrong?
Thanks in advance!
Burak