Demo gives error

1

I installed Fenics and then tried to run the Poisson example code from here.

I get this error:
KeyError: ‘Must supply element or degree’.

The problem was solved upon changing:

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

to

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

However, if I try run another demo from here, I get this error:

TypeError: unsupported operand type(s) for *: ‘FunctionSpace’ and ‘FunctionSpace’

Is there a difference between the current available Fenics and the documentation? It seems something in Fenics has changed but is not reflected in the documentation.

1 Like
2

Hi
the link you mentioned refer to version 1.3 of FEniCS which is extremely old so that a few things have changed in the API, in particular the definition of MixedFunctionSpace using the star operator. The current demos can be found here https://fenicsproject.org/docs/dolfin/2019.1.0/python/demos.html

3 Likes
3

Ironically, this link is now broken

4

Consider: Demos — DOLFIN documentation
or simply:
Bitbucket

5

The first link lists demos, one of which has (I think) the same problem as before:

https://fenicsproject.org/olddocs/dolfin/latest/python/demos/mixed-poisson/demo_mixed-poisson.py.html

6

I am not sure which link you are referring to.
The link you have provided works. and I cannot see which link inside the reference I provided that you mean is incorrect

7

To be clear:

https://fenicsproject.org/olddocs/dolfin/latest/python/demos.html

has a link to:

https://fenicsproject.org/olddocs/dolfin/latest/python/demos/mixed-poisson/demo_mixed-poisson.py.html

which doesn’t work

8

i.e., this link:

Demos — DOLFIN documentation

9

The latest link you are sending is directing me to a workin webpage, which has the following link:

image
image828×1792 236 KB

This link sends me to the demo:
image
image828×1792 126 KB

This link also sends me to the demo

10

The demo doesn’t work. That’s what I meant

11

What error do you obtain when running the demo?

12

Aha! I found the problem – at my end. I was running an out-of-date version of “demo_mixed-poisson.py”, not the one pointed to by that link. Apologies!

FWIW, and for those of us who are new here and haven’t seen the evolution of the Dolfin over time, this works:

BDM = FiniteElement("BDM", mesh.ufl_cell(), 1)
DG  = FiniteElement("DG", mesh.ufl_cell(), 0)
W = FunctionSpace(mesh, BDM * DG)

but this doesn’t (any more):

BDM = FunctionSpace(mesh, "BDM", 1)
DG = FunctionSpace(mesh, "DG", 0)
W = BDM * DG