# Demo code not working using my installation of FEniCS

**URL:** <https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180>\
**Category:** installation\
**Created:** [February 11, 2019, 6:46am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180 "2019-02-11T06:46:17Z")\
**Posts on this page:** 10\
**Page:** 1

<div class="post-metadata">

**Author:** ![Athul\_Shaji](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/athul_shaji/32/456_2.png) [@Athul\_Shaji](https://fenicsproject.discourse.group/u/Athul_Shaji)\
**Post date:** [February 11, 2019, 6:46am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/1 "2019-02-11T06:46:18Z")

</div>

Hello,

My name is Athul Shaji, a researcher from India. I have the following problem while using FEniCS.

I had installed FEniCS in Ubuntu 18.04.1. The laptop has 8GB RAM and Core i3 7100 processor. I am getting error messages the demo codes provided the FEniCS webpage is run. The IDE used is Spyder. **I am not using Anaconda package.** The different packages like Spyder, Numpy, Scipy, and Matplotlib are installed using pip. **I have installed FEniCS project 2018.1.0**.

The code which I tried to run is as follows:

```
import matplotlib.pyplot as plt
from fenics import *

class DirichletBoundary(SubDomain):
    def inside(self, x, on_boundary):
        return abs(x[0] - 1.0) < DOLFIN_EPS and on_boundary

mesh = UnitSquareMesh(32, 32)
File("mesh.pvd") << mesh

V = FunctionSpace(mesh, "CG", 1)

g = Constant(1.0)
bc = DirichletBC(V, g, DirichletBoundary())

u = Function(V)
v = TestFunction(V)
f = Expression("x[0]*sin(x[1])", degree=2)
F = inner((1 + u**2)*grad(u), grad(v))*dx - f*v*dx

solve(F == 0, u, bc,
      solver_parameters={"newton_solver":{"relative_tolerance":1e-6}})

plt.figure()
plot(u, title="Solution")

plt.figure()
plot(grad(u), title="Solution gradient")
plt.show()
file = File("nonlinear_poisson.pvd")
file << u

```

**The error message obtained when I ran the program is as follows:**

```
athul@athul-X510UA:~/Desktop$ python3 nonlinearpoisson.py 
Calling FFC just-in-time (JIT) compiler, this may take some time.
Traceback (most recent call last):
  File "nonlinearpoisson.py", line 134, in <module>
    V = FunctionSpace(mesh, "CG", 1)
  File "/usr/lib/python3/dist-packages/dolfin/function/functionspace.py", line 33, in __init__
    self._init_convenience(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/dolfin/function/functionspace.py", line 100, in _init_convenience
    self._init_from_ufl(mesh, element, constrained_domain=constrained_domain)
  File "/usr/lib/python3/dist-packages/dolfin/function/functionspace.py", line 43, in _init_from_ufl
    mpi_comm=mesh.mpi_comm())
  File "/usr/lib/python3/dist-packages/dolfin/jit/jit.py", line 47, in mpi_jit
    return local_jit(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/dolfin/jit/jit.py", line 97, in ffc_jit
    return ffc.jit(ufl_form, parameters=p)
  File "/usr/lib/python3/dist-packages/ffc/jitcompiler.py", line 217, in jit
    module = jit_build(ufl_object, module_name, parameters)
  File "/usr/lib/python3/dist-packages/ffc/jitcompiler.py", line 133, in jit_build
    generate=jit_generate)
  File "/usr/lib/python3/dist-packages/dijitso/jit.py", line 165, in jit
    header, source, dependencies = generate(jitable, name, signature, params["generator"])
  File "/usr/lib/python3/dist-packages/ffc/jitcompiler.py", line 66, in jit_generate
    prefix=module_name, parameters=parameters, jit=True)
  File "/usr/lib/python3/dist-packages/ffc/compiler.py", line 150, in compile_element
    prefix, parameters, jit)
  File "/usr/lib/python3/dist-packages/ffc/compiler.py", line 190, in compile_ufl_objects
    ir = compute_ir(analysis, prefix, parameters, jit)
  File "/usr/lib/python3/dist-packages/ffc/representation.py", line 168, in compute_ir
    for e in elements]
  File "/usr/lib/python3/dist-packages/ffc/representation.py", line 168, in <listcomp>
    for e in elements]
  File "/usr/lib/python3/dist-packages/ffc/representation.py", line 200, in _compute_element_ir
    fiat_element = create_element(ufl_element)
  File "/usr/lib/python3/dist-packages/ffc/fiatinterface.py", line 99, in create_element
    element = _create_fiat_element(ufl_element)
  File "/usr/lib/python3/dist-packages/ffc/fiatinterface.py", line 192, in _create_fiat_element
    element = ElementClass(fiat_cell, degree)
  File "/usr/lib/python3/dist-packages/FIAT/lagrange.py", line 54, in __init__
    poly_set = polynomial_set.ONPolynomialSet(ref_el, degree)
  File "/usr/lib/python3/dist-packages/FIAT/polynomial_set.py", line 174, in __init__
    dv = expansion_set.tabulate_derivatives(degree, pts)
  File "/usr/lib/python3/dist-packages/FIAT/expansions.py", line 260, in tabulate_derivatives
    data = _tabulate_dpts(self._tabulate, 2, n, order, numpy.array(pts))
  File "/usr/lib/python3/dist-packages/FIAT/expansions.py", line 102, in _tabulate_dpts
    phi.append(form_derivative(phi[-1]))
  File "/usr/lib/python3/dist-packages/FIAT/expansions.py", line 48, in form_derivative
    out = [sympy.diff(F, X[j]) for j in range(D)]
  File "/usr/lib/python3/dist-packages/FIAT/expansions.py", line 48, in <listcomp>
    out = [sympy.diff(F, X[j]) for j in range(D)]
  File "/home/athul/.local/lib/python3.6/site-packages/sympy/core/function.py", line 1979, in diff
    return Derivative(f, *symbols, **kwargs)
  File "/home/athul/.local/lib/python3.6/site-packages/sympy/core/function.py", line 1121, in __new__
    it cannot be differentiated.''' % expr))
ValueError: 
Since there are no variables in the expression [0, 0], it cannot be
differentiated.

```

Please help me with this error. Thank you.

Athul Shaji

---

<div class="post-metadata">

**Author:** ![johannr](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/johannr/32/13_2.png) [@johannr](https://fenicsproject.discourse.group/u/johannr)\
**Post date:** [February 11, 2019, 1:27pm UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/2 "2019-02-11T13:27:46Z")

</div>

Hi,

Your post is difficult to read because you have not formatted the code correctly - please do that ([Read before posting: How do I get my question answered?](https://fenicsproject.discourse.group/t/read-before-posting-how-do-i-get-my-question-answered/21)).

Also, I do not see an error message, only a `RuntimeWarning`.

Note that installing NumPy via pip will most likely not work if you are using the FEniCS Ubuntu packages, because these packages are already linked to a specific version of NumPy.

---

<div class="post-metadata">

**Author:** ![Athul\_Shaji](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/athul_shaji/32/456_2.png) [@Athul\_Shaji](https://fenicsproject.discourse.group/u/Athul_Shaji)\
**Post date:** [February 11, 2019, 1:56pm UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/3 "2019-02-11T13:56:40Z")

</div>

Hi, I have edited the code so it is more readable. Please have a look at the error message generated when the I tried to execute the code from the terminal of the Linux machine. Looking forward to your reply.

Thank you.

---

<div class="post-metadata">

**Author:** ![Rudy](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/rudy/32/94_2.png) [@Rudy](https://fenicsproject.discourse.group/u/Rudy)\
**Post date:** [February 11, 2019, 8:08pm UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/4 "2019-02-11T20:08:35Z")

</div>

Athul,

Your example works just fine on my Linux machine, version 2018.1.0. You may want to take a look at the FEniCS support group on Google ([https://groups.google.com/forum/?nomobile=true#!forum/fenics-support](https://groups.google.com/forum/?nomobile=true#!forum/fenics-support)) where people have reported the same bug. Personally, I would recommend installing FEniCS either using Anaconda or Docker.

Good luck,

Rudy.

---

<div class="post-metadata">

**Author:** ![Athul\_Shaji](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/athul_shaji/32/456_2.png) [@Athul\_Shaji](https://fenicsproject.discourse.group/u/Athul_Shaji)\
**Post date:** [February 12, 2019, 2:48am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/5 "2019-02-12T02:48:14Z")

</div>

Hi Rudy,

Have you installed FEniCS using Anaconda or Docker? If yes, then I will try to install the software in the same manner in my machine.

Athul Shaji

---

<div class="post-metadata">

**Author:** ![Rudy](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/rudy/32/94_2.png) [@Rudy](https://fenicsproject.discourse.group/u/Rudy)\
**Post date:** [February 12, 2019, 3:05pm UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/6 "2019-02-12T15:05:10Z")

</div>

Athul,

Choosing which prebuilt package you adopt for your research is a very personal choice as both Docker and Anaconda installations work great on Linux machines (including Ubuntu 18.04). My recommendation for the less experienced user is Anaconda.

Rudy.

---

<div class="post-metadata">

**Author:** ![Athul\_Shaji](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/athul_shaji/32/456_2.png) [@Athul\_Shaji](https://fenicsproject.discourse.group/u/Athul_Shaji)\
**Post date:** [February 13, 2019, 2:00am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/7 "2019-02-13T02:00:58Z")

</div>

Rudy, thanks for the reply.

---

<div class="post-metadata">

**Author:** ![johannr](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/johannr/32/13_2.png) [@johannr](https://fenicsproject.discourse.group/u/johannr)\
**Post date:** [February 15, 2019, 9:15am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/8 "2019-02-15T09:15:11Z")

</div>

The problem is the SymPy version you have installed in `/home/athul/.local/`. This version has a regression bug and does not work with FEniCS 2018.1.0. This is a common problem and the simplest fix is to remove the installation of SymPy in `/home/athul/.local/`.

---

<div class="post-metadata">

**Author:** ![venkat201](https://avatars.discourse-cdn.com/v4/letter/v/ecb155/32.png) [@venkat201](https://fenicsproject.discourse.group/u/venkat201)\
**Post date:** [August 22, 2019, 6:07am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/9 "2019-08-22T06:07:48Z")

</div>

i am getting error like this while running demo code  
hemanth@CMS:~/Documents$ python3 demo\_cahn-hilliard.py  
Traceback (most recent call last):  
File “demo\_cahn-hilliard.py”, line 63, in   
ME = V\*V  
TypeError: unsupported operand type(s) for \*: ‘FunctionSpace’ and ‘FunctionSpace’

---

<div class="post-metadata">

**Author:** ![urbainvaes](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/urbainvaes/32/509_2.png) [@urbainvaes](https://fenicsproject.discourse.group/u/urbainvaes)\
**Post date:** [November 26, 2019, 10:31am UTC](https://fenicsproject.discourse.group/t/demo-code-not-working-using-my-installation-of-fenics/180/10 "2019-11-26T10:31:08Z")

</div>

I am experiencing the same issue as OP on Ubuntu 18.04, but with the system version of Sympy.