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import ufl
from dolfin import *
from dolfin_utils.test import skip_in_parallel
@skip_in_parallel
def test_interior_facet_integral_sides():
n = 1
mesh = UnitSquareMesh(n, n)
markers = MeshFunction("size_t", mesh, mesh.topology().dim())
subdomain = AutoSubDomain(lambda x, on_boundary: x[0] > x[1]-DOLFIN_EPS)
V = FunctionSpace(mesh, "DG", 0)
f = interpolate(Expression("x[0]", degree=1), V)
# Define forms picking value of f from + and - sides
scale = 1.0/ufl.FacetArea(mesh)
Mp = f('+')*scale*dS(domain=mesh)
Mm = f('-')*scale*dS(domain=mesh)
# Hack to attach cell markers to dS integral... Need to find a UFL
# solution to this.
Mh = Constant(0)*dx(99, domain=mesh, subdomain_data=markers)
Mp = Mp + Mh
Mm = Mm + Mh
# Case A: subdomain is 1, rest is 0
markers.set_all(0)
subdomain.mark(markers, 1)
assert abs(assemble(Mp) - 2.0/3.0) < 1e-8
assert abs(assemble(Mm) - 1.0/3.0) < 1e-8
# Case B: subdomain is 0, rest is 1
markers.set_all(1)
subdomain.mark(markers, 0)
assert abs(assemble(Mp) - 1.0/3.0) < 1e-8
assert abs(assemble(Mm) - 2.0/3.0) < 1e-8
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