# [deal.II] Re: multiply constrained dofs (hanging nodes+periodic) fails a simple test case


On Wednesday, April 11, 2018 at 7:00:18 PM UTC+2, Sambit Das wrote:
>
> Hi Denis,
>
>
>> I don't think that's the case. The domain is indeed periodic, but this is
>> completely detached from location of support/nodal points.
>> Same applies to geometry, you will have different coordinates of vertices
>> across the PBC so
>>
>>
> I agree, the location of nodal points is detached from the periodicity of
> the domain, but in this case the origin is at the center of the hypercube.
> This artificially enforces that the nodal_coordinate.norm() is periodic.
>

true, but I don't see why you would have the same norms if you distribute
with constraints from hanging nodes only or constraints from hanging nodes+
PBC.
I think we can agree that the two ConstraintMatrix objects should be
different as in the case of PBC you additionally need to make sure that FE
space on the refined boundary matches that on the opposite, non-refined
side.

If you suspect that there is a bug in constraints, you could check this by
simply choosing some more-or-less random vector, distribute and
plot-over-line in Paraview / Visit.
More cumbersome comparison would be to evaluate random field at the
opposite points.
You can use FEField function and then choose   L/2-\delta  and -L/2+\delta
with \delta = 1e-8 or so for X coordinate and then
whatever you want to Y/Z. This should give you the same value anywhere on
the two periodically matching points for a random input vector after
constraints are distributed.

Denis.

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