Error using the cofac() function of UFL

General
1

Hi everyone,

FEniCS generates an error while using the cofac() function from UFL. Its a simple code where I generate a mesh, create a vector function space, create a function in the vector function space, calculate the identity tensor using the geometric dimension, create a deformation gradient tensor, and then calculate the cofactor of the deformation gradient tensor.

Here is the MWE:

from dolfin import *     
from ufl import cofac

mesh = UnitCubeMesh(24, 16, 16)  # Defining cubic mesh

V = VectorFunctionSpace(mesh, "Lagrange", 1) # Defining order 1 Lagrange Vector Function Space

u = Function(V) # Creating element from V

d = u.geometric_dimension() # Calculating dimension of geometry
I = Identity(d)             # Identity tensor with order of geometric dimension
F = I + grad(u)             # Calculating deformation gradient tensor

cofac_F = cofac(F)          # Calculating cofactor of F

This generates the error:

cofac_F = cofac(F)
  File "/usr/lib/python3/dist-packages/ufl/operators.py", line 218, in cofac
    A = as_ufl(A)
  File "/usr/lib/python3/dist-packages/ufl/constantvalue.py", line 501, in as_ufl
    raise ValueError(
ValueError: Invalid type conversion: I + (grad(f_5)) can not be converted to any UFL type.

What am I doing wrong here?

Please advise.

Thanks in advance!

2

What version of ufl are you using? I cannot reproduce this with the last release of ufl for legacy dolfin (i.e. ufl_legacy) using: docker run -ti -v $(pwd):/root/shared -w /root/shared --rm ghcr.io/scientificcomputing/fenics:2024-02-19

3

I am using Ubuntu. How do I check the version of ufl?

4

python3 -c "import ufl; print(ufl.__version__)"

5

Here is the response:

2023.2.0
6

Any suggestions on how to resolve this issue?

7

It is unclear to me how you have gotten that version of ufl for the Legacy release of Dolfin.
For legacy dolfin you should now use ufl_legacy: Announcement: ufl_legacy and legacy dolfin

8

@dokken Thanks for the explanation. How do I update the version from 2023.2.0 to the one you are referring to in Ubuntu? I am sorry if this is a trivial question. I am not so familiar with ubuntu commands.

Please advise.

Thank you.

9

It’s a separate package. If your dolfin installation is up to date then you’d already have it installed. Check with dpkg -l python3-ufl-legacy

What you need to do is use it,
i.e. replace

from ufl import cofac

with

from ufl_legacy import cofac

That would be current ufl (python3-ufl not python3-ufl-legacy). Steppenwolf’s system would have it alongside ufl_legacy if they also installed dolfinx (fenicsx) alongside dolfin.

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