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[Marie Rognes <meg@xxxxxxxxxxx>]

The following piece of code, which defines a source that only has 
non-zero values on one part of the boundary and assembles this source on 
the boundary,



   from dolfin import *


   class BoundarySource(Function):
       def __init__(self, element, mesh):
           Function.__init__(self, element, mesh)
       def eval(self, values, x):
           values[0] = 0.0
           if abs(x[0] - 1.0) < DOLFIN_EPS:
                   values[0] = 1.0

   mesh = UnitSquare(3, 3)

   element = FiniteElement("DG", "triangle", 0)
   f = BoundarySource(element, mesh)
   v = TestFunction(element)
   L = f*v*ds

   rhs = assemble(L, mesh)
   print "norm of L = ", rhs.norm()



gives output

    norm of L =  0.0


Is this expected?

Changing element to continuous/discontinuous linears gives non-zero 
values...

--
Marie E. Rognes
Ph.D Fellow, 
Centre of Mathematics for Applications, 
University of Oslo
http://folk.uio.no/meg