# Temperature export in discontinuous problem

**URL:** <https://festim.discourse.group/t/temperature-export-in-discontinuous-problem/162>\
**Category:** User Support\
**Created:** [April 15, 2026, 2:34pm UTC](https://festim.discourse.group/t/temperature-export-in-discontinuous-problem/162 "2026-04-15T14:34:10Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![tez0rr](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/tez0rr/32/267_2.png) [@tez0rr](https://festim.discourse.group/u/tez0rr)\
**Post date:** [April 15, 2026, 2:34pm UTC](https://festim.discourse.group/t/temperature-export-in-discontinuous-problem/162/1 "2026-04-15T14:34:10Z")

</div>

Hi,

VTXTemperatureExport object does not seem to be implemented for the discontinuous case. I run into the error:

> NotImplementedError: Export type \<class ‘festim.exports.vtx.VTXTemperatureExport’\> not implemented

When running the following:

```auto
import festim as F
import numpy as np

my_model = F.HydrogenTransportProblemDiscontinuous()

mat = F.Material(
    D_0=1,
    E_D=0,
)

vol = F.VolumeSubdomain1D(id=1, borders=[0, 1], material=mat)

my_model.subdomains = [vol]

my_model.mesh = F.Mesh1D(np.linspace(0, 1, 100))

my_model.species = [F.Species("H", subdomains=[vol])]

my_model.temperature = 700

my_model.settings = F.Settings(transient=False, atol=1e-9, rtol=1e-9)

temp_export = F.VTXTemperatureExport(
    filename="mwe_exports/temperature.bp",
)

my_model.exports = [temp_export]

my_model.initialise()

my_model.run()

```

---

<div class="post-metadata">

**Author:** ![remidm](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/remidm/32/4_2.png) [@remidm](https://festim.discourse.group/u/remidm)\
**Post date:** [April 17, 2026, 12:34pm UTC](https://festim.discourse.group/t/temperature-export-in-discontinuous-problem/162/2 "2026-04-17T12:34:16Z")

</div>

Note: please format your code correctly with triple signs ``` and not quote blocks `>`. I modified your post

I reproduce the error

```auto
Traceback (most recent call last):
  File "/home/remidm/FESTIM/mwe.py", line 40, in <module>
    my_model.run()
  File "/home/remidm/FESTIM/src/festim/hydrogen_transport_problem.py", line 1861, in run
    self.post_processing()
  File "/home/remidm/FESTIM/src/festim/hydrogen_transport_problem.py", line 1708, in post_processing
    raise NotImplementedError(
NotImplementedError: Export type <class 'festim.exports.vtx.VTXTemperatureExport'> not implemented

```

This is because we have not yet implemented the VTXTemperatureExport support in the `HydrogenTransportProblemDiscontinuous` class.

Now in your case you can manually export the temperature at the end of the simulation (or maybe even just after `initialise()`

```python
import festim as F
import numpy as np

my_model = F.HydrogenTransportProblemDiscontinuous()

mat = F.Material(
    D_0=1,
    E_D=0,
)

vol = F.VolumeSubdomain1D(id=1, borders=[0, 1], material=mat)

my_model.subdomains = [vol]

my_model.mesh = F.Mesh1D(np.linspace(0, 1, 100))

my_model.species = [F.Species("H", subdomains=[vol])]

# Had to change this because it only makes sense to export the temperature
# to a file if it's a function of x and not a constant.
my_model.temperature = lambda x: 700 + 100 * x[0]

my_model.settings = F.Settings(transient=False, atol=1e-9, rtol=1e-9)

# temp_export = F.VTXTemperatureExport(
# filename="mwe_exports/temperature.bp",
# )

# my_model.exports = [temp_export]

my_model.initialise()
my_model.run()

from dolfinx import fem
from dolfinx.io import VTXWriter
from mpi4py import MPI
from pathlib import Path

assert isinstance(my_model.temperature_fenics, fem.Function), (
    f"Temperature field is not a fenics function, got {type(my_model.temperature_fenics)}"
)

with VTXWriter(
    MPI.COMM_WORLD,
    Path("mwe_exports/temperature.bp"),
    my_model.temperature_fenics,
    "BP4",
) as writer:
    writer.write(0.0)

```

Opening `temperature.bp` in Paraview:

 ![image](https://global.discourse-cdn.com/free1/uploads/festim/original/1X/07361ab2b5418473eb05265a32bbcbbbf6ace720.png)