Exterior facet assembly does not detect the sparsity pattern

[corrado maurini]

Hi,

I suspect that the exterior facet assembly does not detect the sparsity pattern.
The code to reproduce this is reported below.
I cannot find any reference to the case "exterior facets" in SparsityPatternBuilder.cpp, see:
http://bazaar.launchpad.net/~dolfin-core/dolfin/trunk/view/head:/dolfin/fem/SparsityPatternBuilder.cpp

May you please validate or invalidate this bug?
Thanks for your help.

Corrado
--------------------------
from dolfin import *
set_log_level(DEBUG)
mesh = UnitSquare(4,4)
V = VectorFunctionSpace(mesh, "CG", 1)
u = TrialFunction(V)
v = TestFunction(V)

# This create a matrix with zeros
assemble(inner(u,v)*dx)

# This create a matrix without zeros
assemble(inner(u,v)*ds)
-------------------------------

[Johan Hake (johan-hake)]

A hackish work around is to assemble a a matrix using the first form and then reuse the matrix while assemble the second one.