dolfin team mailing list archive

[Marie Rognes <meg@xxxxxxxxx>]

There is something suboptimal with regard to assembly over sub_domains 
specified
by domains (in contrast to markers)

Say I have some functional

(*)    M = f*ds

where f is some function. Let 'domain' be some sub-domain.

Now, it is not clear to me what

   v = assemble(M, mesh=mesh, exterior_facet_domains=domain)

gives. It would be really convenient (for my purposes) if it gave
the same as

   v = assemble(M, mesh=mesh)

It would also make some sense, considering that no special
tag has been defined in (*), and so the exterior_facet_domains
argument could be ignored.

It does not at the moment though. At the moment, it seems
as though ds -> ds(0) and the sub-domain is converted
to markers, marking anything inside 'domain' as 0, and
everything else as 1...?  This is really not obvious to me.

Could "we" change the interface to something slightly
more transparent?

--
Marie


PS: Example attached.



from dolfin import *

class Domain(SubDomain):
   def inside(self, x, on_boundary):
       return x[0] < 0.5 and on_boundary

mesh = UnitSquare(8, 8)
f = Expression("sin(pi*x[0])")
M = f*ds

domain = Domain()

markers = MeshFunction("uint", mesh, 1)
markers.set_all(0)
domain.mark(markers, 1)

v1 = assemble(M, mesh=mesh)
v2 = assemble(M, mesh=mesh, exterior_facet_domains=domain)
v3 = assemble(M, mesh=mesh, exterior_facet_domains=markers)

print "It is not intuitive what these become ..."
print "v1 = ", v1
print "v2 = ", v2
print "v3 = ", v3