PeriodicBC problem

Hi,

I think you missed your channel's boundary. Here is an example how I connected left and right side of a UnitSquare [0,1]**2:

class BoundaryHorz(SubDomain):
    def inside(self, x, on_boundary):
        return bool(x[0] < DOLFIN_EPS and x[0] > -DOLFIN_EPS and on_boundary)
    def map(self, y, x):
        x[0] = y[0] - 1.0
        x[1] = y[1]

Thomas

I am having a similar problem in 1D. Here is the sample code

from dolfin import *
from numpy import pi

n = 339

mesh = Interval(n, 0, 2*pi)
V = FunctionSpace(mesh, 'Lagrange', 1)

class PerBcs(SubDomain):
    def inside(self, x, on_boundary):
        return bool(x[0] < DOLFIN_EPS and
                    x[0] > -DOLFIN_EPS and
                    on_boundary)
    def map(self, x, y):
        y[0] = x[0] - 2*pi

pbc = PerBcs()
bcs = PeriodicBC(V, pbc)

The code works for n=340 and it also works if one replaces the replaces 2*pi by 6.28318530717958, which is 2*pi with the last digit set to 0. The error message I get is

Building mapping between periodic degrees of freedom.
At coordinate: x = 0
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)

/home/martins/diss/prog/kurtek/p/<ipython console> in <module>()

/home/martins/diss/prog/kurtek/p/dolfin_bug.py in <module>()
     26
     27 pbc = PerBcs()
---> 28 bcs = PeriodicBC(V, pbc)
     29
     30

/usr/lib/python2.7/dist-packages/dolfin/cpp.pyc in __init__(self, *args)
  19191
  19192 """
> 19193 _cpp.PeriodicBC_swiginit(self,_cpp.new_PeriodicBC(*args))
  19194 __swig_destroy__ = _cpp.delete_PeriodicBC
  19195 def apply(self, *args):

RuntimeError:

*** -------------------------------------------------------------------------
*** DOLFIN encountered an error. If you are not able to resolve this issue
*** using the information listed below, you can ask for help at
***
*** https://answers.launchpad.net/dolfin
***
*** Remember to include the error message listed below and, if possible,
*** include a *minimal* running example to reproduce the error.
***
*** -------------------------------------------------------------------------
*** Error: Unable to apply periodic boundary condition.
*** Reason: Could not find a pair of matching degrees of freedom.
*** Where: This error was encountered inside PeriodicBC.cpp.
*** -------------------------------------------------------------------------

Is this a bug in dolfin due to some rounding errors?