Assembly produces erraneous results when mesh comes from csg Circle

[Andreas Hellander]

When assembling the stiffness matrix for a mesh created with dolfin.Circle, the resulting matrix contains huge values (for radius 1) or even "nan" (for radius different from 1). Here is an example that will reproduce the problem. Visually, the mesh looks fine with no apparent very bad elements.

This error started to appear after I upgraded to Dolfin 1.3.0 and I have confirmed this behaviour on OSX 10.8 and Linux Mint Maya (Ubuntu). Here is a the test I ran

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import dolfin
dolfin.parameters["linear_algebra_backend"] = "uBLAS"

import numpy

c = dolfin.Circle(0,0,1)
mesh = dolfin.Mesh(c,20)

function_space = dolfin.FunctionSpace(mesh,"Lagrange",1)
trial_function = dolfin.TrialFunction(function_space)
test_function = dolfin.TestFunction(function_space)

form = dolfin.inner(dolfin.nabla_grad(trial_function), dolfin.nabla_grad(test_function))*dolfin.dx
K = dolfin.assemble(form)
rows, cols, vals = K.data()
print numpy.max(vals)

[Johannes Ring (johannr)]

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