# What is the current equivalent of =ufl.VectorElement= with =dolfinx.fem.FunctionSpace=?

**URL:** <https://fenicsproject.discourse.group/t/what-is-the-current-equivalent-of-ufl-vectorelement-with-dolfinx-fem-functionspace/12386>\
**Category:** General\
**Created:** [October 5, 2023, 2:39pm UTC](https://fenicsproject.discourse.group/t/what-is-the-current-equivalent-of-ufl-vectorelement-with-dolfinx-fem-functionspace/12386 "2023-10-05T14:39:29Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![edgar](https://avatars.discourse-cdn.com/v4/letter/e/b487fb/32.png) [@edgar](https://fenicsproject.discourse.group/u/edgar)\
**Post date:** [October 5, 2023, 2:39pm UTC](https://fenicsproject.discourse.group/t/what-is-the-current-equivalent-of-ufl-vectorelement-with-dolfinx-fem-functionspace/12386/1 "2023-10-05T14:39:29Z")

</div>

Hello,

# Short description

The [DOLFINx tutorial](https://github.com/jorgensd/dolfinx-tutorial.git)  
([c9214c68438ab27d2fa8936307027c5209272162](https://github.com/jorgensd/dolfinx-tutorial/blob/c9214c68438ab27d2fa8936307027c5209272162/chapter2/linearelasticity_code.ipynb))  
mentions that

> creating a vector element `element = ufl.VectorElement(\“CG\”,  
> mesh.ufl~cell~(), 1) … , and intitializing the function space as `V  
> = dolfinx.fem.FunctionSpace(mesh, element)`

# Current behaviour

However, trying that combination:

```example
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'dolfinx.mesh' has no attribute 'ufl_cell'

```

# What I have tried (not working either)

I also tried with

```python
element = basix.ufl.element("Lagrange", basix.CellType.hexahedron, 1)
V = dolfinx.fem.FunctionSpace(mesh, element)

```

```example
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.11/site-packages/dolfinx/fem/function.py", line 581, in FunctionSpace
    return functionspace(mesh, element, form_compiler_options, jit_options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/dolfinx/fem/function.py", line 527, in functionspace
    if ufl_e.cell() != mesh.ufl_domain().ufl_cell():
                       ^^^^^^^^^^^^^^^
AttributeError: module 'dolfinx.mesh' has no attribute 'ufl_domain'

```

and

```python
fem.FunctionSpace(ufl.VectorElement("Lagrange", ufl.hexahedron, 1))

```

```example
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.11/site-packages/dolfinx/fem/function.py", line 581, in FunctionSpace
    return functionspace(mesh, element, form_compiler_options, jit_options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/site-packages/dolfinx/fem/function.py", line 527, in functionspace
    if ufl_e.cell() != mesh.ufl_domain().ufl_cell():
                       ^^^^^^^^^^^^^^^
AttributeError: module 'dolfinx.mesh' has no attribute 'ufl_domain'

```

# MWE

```python
import dolfinx
import basix
from dolfinx import fem
from dolfinx import mesh
from mpi4py import MPI

element = basix.ufl.element("Lagrange", basix.CellType.hexahedron, 1)
V = dolfinx.fem.FunctionSpace(mesh, element)

```

# My system

```example
* FEniCSx software
dolfinx: 0.7.0.dev0_r27554.cfeffe0-1
basix: 0.7.0.dev0_r945.1117a8d-1
ufl: 2023.2.0.dev0_r3562.77ae57c-1
ffcx: 0.7.0.dev0_r7077.1d27238-1

* Dependencies
python: 3.11.5-2
python-numpy: 1.26.0-1
petsc: 3.19.5.1171.g37df9106526-1
hdf5-openmpi: 1.14.2-1
boost: 1.83.0-2
adios2: 2.8.3-5
scotch: 7.0.4-1
pybind11: 2.11.1-1
python-build: 1.0.1-1
python-cffi: 1.15.1-4
python-cppimport: 22.08.02.r6.g0849d17-1
python-installer: 0.7.0-3
python-mpi4py: 3.1.4-3
python-pytest: 7.4.2-1
python-scikit-build: 0.17.6-1
python-setuptools: 1:68.0.0-1
python-wheel: 0.40.0-3
xtensor: 0.24.0-2
xtensor-blas: 0.20.0-1

* Operating system
Arch Linux: 6.5.4-arch2-1

```

---

<div class="post-metadata">

**Author:** ![nate](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/nate/32/17_2.png) [@nate](https://fenicsproject.discourse.group/u/nate)\
**Post date:** [October 5, 2023, 3:18pm UTC](https://fenicsproject.discourse.group/t/what-is-the-current-equivalent-of-ufl-vectorelement-with-dolfinx-fem-functionspace/12386/2 "2023-10-05T15:18:54Z")

</div>

Your `mesh` variable refers to the python module `dolfinx.mesh`, and not an actual `dolfinx.mesh.Mesh` instance. E.g.

```python
import dolfinx
import basix
from dolfinx import fem
from dolfinx import mesh
from mpi4py import MPI

element = basix.ufl.element("Lagrange", basix.CellType.hexahedron, 1)
mesh = dolfinx.mesh.create_unit_cube(MPI.COMM_WORLD, 1, 1, 1, cell_type=dolfinx.mesh.CellType.hexahedron)
V = dolfinx.fem.FunctionSpace(mesh, element)

```

---

<div class="post-metadata">

**Author:** ![edgar](https://avatars.discourse-cdn.com/v4/letter/e/b487fb/32.png) [@edgar](https://fenicsproject.discourse.group/u/edgar)\
**Post date:** [October 5, 2023, 5:57pm UTC](https://fenicsproject.discourse.group/t/what-is-the-current-equivalent-of-ufl-vectorelement-with-dolfinx-fem-functionspace/12386/3 "2023-10-05T17:57:46Z")

</div>

Oh, ok. Thanks! That makes a lot of sense (to not use a module as in input parameter \>.\<). It also shows why the convenience function exists (2 shorter lines of code compared to 3 longer lines).

Is there any advantage of doing it as you showed? (compared to what is shown in the tutorial):

```python
domain = mesh.create_box(MPI.COMM_WORLD, [np.array([0,0,0]), np.array([L, W, W])],
                  [20,6,6], cell_type=mesh.CellType.hexahedron)
V = fem.VectorFunctionSpace(domain, ("CG", 1))

```

---

<div class="post-metadata">

**Author:** ![nate](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/nate/32/17_2.png) [@nate](https://fenicsproject.discourse.group/u/nate)\
**Post date:** [October 5, 2023, 6:48pm UTC](https://fenicsproject.discourse.group/t/what-is-the-current-equivalent-of-ufl-vectorelement-with-dolfinx-fem-functionspace/12386/4 "2023-10-05T18:48:16Z")

</div>

The `basix` path provides much more control/power for custom elements and quadrature schemes. If you want a “fire and forget” continuous Galerkin basis on hexes, the method you’ve used immediately above is perfectly sufficient.