Discretizing robin boundary conditions on a RectGrid

[deneick]

Currently discretizing a problem with a robin boundary condition on a RectGrid raises a NotImplementedError. Replacing NI = bi.neumann_boundaries(1) in line 310 in operators.cg with NI = bi.boundaries(self.boundary_type, 1) if self.boundary_type else g.boundaries(1) as in line 136 worked as a fix for me.
Since then BoundaryL2ProductFunctionalP1 and BoundaryL2ProductFunctionalQ1 are basically the same, it might be an idea to have just one BoundaryL2ProductFunctional.

Example:

from pymor.basic import *
from pymor.grids.rect import RectGrid
domain=RectDomain(bottom='robin')
p = StationaryProblem(domain=domain,
diffusion=ConstantFunction(1, dim_domain=domain.dim),
robin_data=(ConstantFunction(1, dim_domain=domain.dim), ConstantFunction(1, dim_domain=domain.dim))
)
d,data = discretize_stationary_cg(p, .1, grid_type=RectGrid)

[sdrave]

@deneick, you are totally right. Thanks for the fix!