Can't run example: KeyError: 'Must supply element or degree'

installation
1

Hello!
I’ve installed fenics on Ubuntu system from ppa repository following instructions from the site. I’m trying to run the basic Poisson example but getting an error:

$ python3 demo_poisson.py 
Traceback (most recent call last):
  File "demo_poisson.py", line 54, in <module>
    f = Expression("10*exp(-(pow(x[0] - 0.5, 2) + pow(x[1] - 0.5, 2)) / 0.02)")
  File "/usr/lib/python3/dist-packages/dolfin/function/expression.py", line 409, in __init__
    raise KeyError("Must supply element or degree")
KeyError: 'Must supply element or degree'

Am I missing something?

2

Yes. Looks like you’ve copied an old example from a previous version of dolfin.

You need to supply the polynomial approximation order degree=2 which sets up a CG space approximation for you, or a specific finite element element=some_element_of_your_choosing.

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