Mixed function space with tensors

variational formulation
1

Hi, I have some problems with the definition of mixed functional space and I’m doing wrong something about the code. I need a mixed functional space with elements like [u,F_v1,…F_vn] where u is a vector in 2D and Fv_i are 2x2 tensors.

from dolfin import *
from mshr import*
import ufl
from ufl import ln
import numpy as np

plt.rcParams[‘axes.formatter.useoffset’] = False
parameters[“form_compiler”][“cpp_optimize”] = True
parameters[“form_compiler”][“representation”] = “uflacs”
ffc_options = {“optimize”: True,
“eliminate_zeros”: True,
“precompute_basis_const”: True,
“precompute_ip_const”: True}
metadata = {“quadrature_degree”: 4}

#################Geometry2D#############################
domain=Rectangle(Point(0,0),Point(lpx,lpy))
mesh=generate_mesh(domain, n_mesh)

#Function spaces

n_kelvin=2 # number of kelvin’s elements

u_build=VectorElement(‘P’,mesh.ufl_cell(),1,2)
Fv_build=TensorElement(‘P’,mesh.ufl_cell(),1)
elements_build=[u_build]
only_viscous_def=
for i in range(n_kelvin):
elements_build.append(Fv_build)
only_viscous_def.append(Fv_build)

Space_vec=MixedFunctionSpace(space_build)
only_viscous_space=MixedFunctionSpace(only_viscous_space)

state_var=Function(Space_vec)
state_var_Trial=TrialFunction(Space_vec)
state_var_Test=TestFunction(Space_vec)

The error message is
RuntimeError: Cannot create product of function spaces, expecting a list of function spaces

Thank you so much!

1 Like
2

I think the MixedFunctionSpace function is expecting a list of arguments. Can you try replacing the calls by:

Space_vec=MixedFunctionSpace(*space_build)

and


only_viscous_space=MixedFunctionSpace(*only_viscous_space)

?

3

Thank you, now the error is state_var_Trial:

TypeError: \ When constructing an Argument, TestFunction or TrialFunction, you
must to provide a FunctionSpace and not a FiniteElement. The
FiniteElement class provided by ufl only represents an abstract finite
element space and is only used in standalone .ufl files, while the
FunctionSpace provides a full discrete function space over a given
mesh and should be used in dolfin programs in Python.

4

I’ve had the same problems as you. You are missing an “s”. Try TrialFunctions and TestFunctions instead of TrialFunction and TestFunction

(these return a list so you can unpack them if you want)

1 Like
5

Perfect, now it works, thank you so much.
Excuse me if I disturb you yet, but when I apply the boundary conditions by

Space_vec.sub(0)

it give:
AttributeError: ‘MixedFunctionSpace’ object has no attribute ‘sub’

6

I not really sure about this, but I think that you are trying to use a MixedFunctionSpace as a VectorFunctionSpace.

The different functions of a MixedFunctionSpace can be accessed as a list, like:

MS = MixedFunctionSpace( V, V ) 
f, g = TestFunctions(MS)
7

Can anyone please help how to resolve this error

8

Please provide a minimal reproducible example of your error, using appropriate code blocks

```python
#add example reproducing error here
```
10

Dear @Swetha_Sri_Nakka_me2 ,

You have not followed my advice of making a minimal, reproducible example that one can copy-paste and get your error message. Therefore, I cannot help you further.

I would advice you to look at mixed-dimensional-examples/Stokes-Traction/stokes_traction_bcs.py at master · cdaversin/mixed-dimensional-examples · GitHub

1 Like