demo_poison.py TypeError: Expression needs an integer argument 'degree'

Question

When I ran the demo_poison.py https://fenicsproject.org/olddocs/dolfin//1.5.0/python/demo/documented/poisson/python/documentation.html#demo-pde-poisson-python-documentation
I get this error. I hope anybody can help me.

Traceback (most recent call last):
File "-/demo_poisson.py", line 54, in
f = Expression("10*exp(-(pow(x[0] - 0.5, 2) + pow(x[1] - 0.5, 2)) / 0.02)")
File "/usr/lib/python2.7/dist-packages/dolfin/functions/expression.py", line 157, in init
element = _auto_select_element_from_shape(value_shape, degree, cell)
File "/usr/lib/python2.7/dist-packages/dolfin/functions/expression.py", line 888, in _auto_select_element_from_shape
raise TypeError("Expression needs an integer argument 'degree' if no 'element' is provided.")
TypeError: Expression needs an integer argument 'degree' if no 'element' is provided.
Aborted

Answer 1

Add the keyword degree=2 when creating the Expression's:

f = Expression("10*exp(-(pow(x[0] - 0.5, 2) + pow(x[1] - 0.5, 2)) / 0.02)", degree=2)
g = Expression("sin(5*x[0])", degree=2)

That said, you are using a version of FEniCS that is not compatible with the demo you are looking at (version 1.5.0). You should make sure that the documentation you are reading matches the version of FEniCS that you are using.