# \#io **URL:** https://fenicsproject.discourse.group/tag/io/3.md [Latest](https://fenicsproject.discourse.group/latest.md) · [Categories](https://fenicsproject.discourse.group/categories.md) · [Tags](https://fenicsproject.discourse.group/tags.md) --- ## [Element type mixtures not allowed?](https://fenicsproject.discourse.group/t/element-type-mixtures-not-allowed/18309)
**Author:** [@ormkotta](https://fenicsproject.discourse.group/u/ormkotta)\ **Replies:** 3\ **Last updated:** [September 1, 2026, 12:40pm UTC](https://fenicsproject.discourse.group/t/element-type-mixtures-not-allowed/18309 "2026-09-01T12:40:30Z")
My noob random walk in the world of FEniCS/dolfinx has recently allowed me to generate 2D meshes with gmsh, which I then import with dolfinx.io.gmshio.read\_from\_mesh.I have even managed to get PyVista up and running insi… --- ## [How to extract oriented facet connectivity from a mesh?](https://fenicsproject.discourse.group/t/how-to-extract-oriented-facet-connectivity-from-a-mesh/19797)
**Author:** [@MathPhy42](https://fenicsproject.discourse.group/u/MathPhy42)\ **Replies:** 4\ **Last updated:** [August 14, 2026, 3:22pm UTC](https://fenicsproject.discourse.group/t/how-to-extract-oriented-facet-connectivity-from-a-mesh/19797 "2026-08-14T15:22:23Z")
Hi everyone, I’m trying to extract the (oriented) connectivity array for a surface of my mesh, which can lie on the boundary or be an internal surface as well. I know you can simply get the connectivity array calling f2… --- ## [Time-dependent mesh-output with higher order elements](https://fenicsproject.discourse.group/t/time-dependent-mesh-output-with-higher-order-elements/19788)
**Author:** [@MathPhy42](https://fenicsproject.discourse.group/u/MathPhy42)\ **Replies:** 3\ **Last updated:** [August 6, 2026, 2:00pm UTC](https://fenicsproject.discourse.group/t/time-dependent-mesh-output-with-higher-order-elements/19788 "2026-08-06T14:00:56Z")
Hi everyone, I want to use some ALE-method with remeshing, but I have problems writing my velocity field, which is composed of second order Lagrange-elements, in a single output file. I have tried all 3 types of writer… --- ## [Mesh cannot run due to TypeError](https://fenicsproject.discourse.group/t/mesh-cannot-run-due-to-typeerror/19605)
**Author:** [@yjin6](https://fenicsproject.discourse.group/u/yjin6)\ **Replies:** 4\ **Last updated:** [March 19, 2026, 1:39am UTC](https://fenicsproject.discourse.group/t/mesh-cannot-run-due-to-typeerror/19605 "2026-03-19T01:39:10Z")
Dear all, my dolfinx.mesh cannot work even for the simplest unit interval mesh generation. Here is the code: from mpi4py import MPI import numpy as np import ufl from dolfinx import mesh comm = MPI.COMM\_WORLD nx … --- ## [How to know the maximum and minumum values of DG solution without plotting?](https://fenicsproject.discourse.group/t/how-to-know-the-maximum-and-minumum-values-of-dg-solution-without-plotting/19521)
**Author:** [@frog](https://fenicsproject.discourse.group/u/frog)\ **Replies:** 1\ **Last updated:** [February 21, 2026, 10:16am UTC](https://fenicsproject.discourse.group/t/how-to-know-the-maximum-and-minumum-values-of-dg-solution-without-plotting/19521 "2026-02-21T10:16:56Z")
Hi, My question does not particularly belong to specific problems. When solving a PDE using CG FEM, since the basis functions are defined as 1 at each vertex, the DOFs are actually solution values. However, since DG bas… --- ## [Paraview crash when opening xdmf file](https://fenicsproject.discourse.group/t/paraview-crash-when-opening-xdmf-file/18408)
**Author:** [@federicobetti](https://fenicsproject.discourse.group/u/federicobetti)\ **Replies:** 3\ **Last updated:** [November 24, 2025, 1:53pm UTC](https://fenicsproject.discourse.group/t/paraview-crash-when-opening-xdmf-file/18408 "2025-11-24T13:53:59Z")
Hello, I have been looking for solutions to this problem on the forum but cannot find anything that works. I am using the dolfinx 0.8.0 docker image and Paraview 5.12.1, I generate a simple xdmf file with the following … --- ## [Solving 3D Stokes problem is killed](https://fenicsproject.discourse.group/t/solving-3d-stokes-problem-is-killed/18370)
**Author:** [@ZhangQi](https://fenicsproject.discourse.group/u/ZhangQi)\ **Replies:** 15\ **Last updated:** [November 16, 2025, 2:09pm UTC](https://fenicsproject.discourse.group/t/solving-3d-stokes-problem-is-killed/18370 "2025-11-16T14:09:58Z")
My dear, thank you very much for your previous assistance. The issue regarding the brain mesh has been resolved. However, the simulation failed due to the excessively dense mesh. To facilitate a better understanding of m… --- ## [Getting exact function values at guass points (query points)](https://fenicsproject.discourse.group/t/getting-exact-function-values-at-guass-points-query-points/18249)
**Author:** [@bagla0](https://fenicsproject.discourse.group/u/bagla0)\ **Replies:** 1\ **Last updated:** [October 3, 2025, 8:53pm UTC](https://fenicsproject.discourse.group/t/getting-exact-function-values-at-guass-points-query-points/18249 "2025-10-03T20:53:06Z")
Dear FEniCSx community, I have solutions over Lagrange functionspace (nodal dofs). However, I want to query the solutions at guass points. Using boxbeam tree- gives a constant value for all points lying in an element. … --- ## [Surface evaluation with correct normal of gmsh mesh](https://fenicsproject.discourse.group/t/surface-evaluation-with-correct-normal-of-gmsh-mesh/18117)
**Author:** [@wurschtbrotwilli](https://fenicsproject.discourse.group/u/wurschtbrotwilli)\ **Replies:** 10\ **Last updated:** [August 25, 2025, 7:01am UTC](https://fenicsproject.discourse.group/t/surface-evaluation-with-correct-normal-of-gmsh-mesh/18117 "2025-08-25T07:01:45Z")
Hello, I’m working on the post-processing of a 3D electrial field (Nedelec elements) problem. I use perfectly matched layers on the surrounding, hence I want to evaluate the electrical field on an interior surface. The … --- ## [Issue with restarting transient simulation with more than one field](https://fenicsproject.discourse.group/t/issue-with-restarting-transient-simulation-with-more-than-one-field/17881)
**Author:** [@theophile-boinnard](https://fenicsproject.discourse.group/u/theophile-boinnard)\ **Replies:** 0\ **Last updated:** [July 3, 2025, 10:04am UTC](https://fenicsproject.discourse.group/t/issue-with-restarting-transient-simulation-with-more-than-one-field/17881 "2025-07-03T10:04:14Z")
Dear Fenicsx community, I am facing an issue when solving coupled time dependent PDEs. I have a code that tries to save, after each successful time step, the fields using adios4dolfinx. However, when I try to restart a… --- ## [Visualizing deformed geometry together with stresses in Paraview](https://fenicsproject.discourse.group/t/visualizing-deformed-geometry-together-with-stresses-in-paraview/17824)
**Author:** [@Philipp\_Weder](https://fenicsproject.discourse.group/u/Philipp_Weder)\ **Replies:** 1\ **Last updated:** [June 23, 2025, 2:56pm UTC](https://fenicsproject.discourse.group/t/visualizing-deformed-geometry-together-with-stresses-in-paraview/17824 "2025-06-23T14:56:20Z")
How can one store the deformation field and the stresses in the same XDMF file such that one can deform the geometry by the deformation field and color the result by the stress field in ParaView? Essentially, I want the… --- ## [Issue importing XDMF file in dolfinx](https://fenicsproject.discourse.group/t/issue-importing-xdmf-file-in-dolfinx/17821)
**Author:** [@Quan](https://fenicsproject.discourse.group/u/Quan)\ **Replies:** 5\ **Last updated:** [June 22, 2025, 7:28pm UTC](https://fenicsproject.discourse.group/t/issue-importing-xdmf-file-in-dolfinx/17821 "2025-06-22T19:28:16Z")
Hi. I’m getting an error when importing an XDMF file. This code has worked well before (3 months ago on a fresh fenicsx installation). Now, I’ve installed fenicsx, and the import doesn’t work anymore. Here is my minimal … --- ## [Visual bug when using Paraview after solving in parallel](https://fenicsproject.discourse.group/t/visual-bug-when-using-paraview-after-solving-in-parallel/17751)
**Author:** [@usiu5555](https://fenicsproject.discourse.group/u/usiu5555)\ **Replies:** 2\ **Last updated:** [June 16, 2025, 2:15am UTC](https://fenicsproject.discourse.group/t/visual-bug-when-using-paraview-after-solving-in-parallel/17751 "2025-06-16T02:15:56Z")
I have prepared an MRE: import dolfinx from mpi4py import MPI from petsc4py import PETSc import numpy as np import ufl from dolfinx.fem.petsc import NonlinearProblem from dolfinx.nls.petsc import NewtonSolver nn = 5 do… --- ## [Use write\_function of xdmf in timeloop in parallel](https://fenicsproject.discourse.group/t/use-write-function-of-xdmf-in-timeloop-in-parallel/17606)
**Author:** [@steffenger](https://fenicsproject.discourse.group/u/steffenger)\ **Replies:** 2\ **Last updated:** [May 14, 2025, 7:41am UTC](https://fenicsproject.discourse.group/t/use-write-function-of-xdmf-in-timeloop-in-parallel/17606 "2025-05-14T07:41:54Z")
Version: fenics-dolfinx 0.9 installed via spack spack add fenics-dolfinx+petsc+adios2 py-fenics-dolfinx cflags="-O3" fflags="-O3" I tried to use fenicsx in parallel and i am confused how to use the write\_function of … --- ## [Subject: KeyError: 0 when Assigning Material Values in FenicsX Code for VCSEL Simulation](https://fenicsproject.discourse.group/t/subject-keyerror-0-when-assigning-material-values-in-fenicsx-code-for-vcsel-simulation/17584)
**Author:** [@LaserM](https://fenicsproject.discourse.group/u/LaserM)\ **Replies:** 1\ **Last updated:** [May 8, 2025, 3:43pm UTC](https://fenicsproject.discourse.group/t/subject-keyerror-0-when-assigning-material-values-in-fenicsx-code-for-vcsel-simulation/17584 "2025-05-08T15:43:05Z")
Dear FenicsX Community, I am currently working on a simulation of a Vertical-Cavity Surface-Emitting Laser (VCSEL) using FenicsX, and I have encountered an issue that I hope the community can help me with. I’ve attached… --- ## [ADIOS2 .bp file error in ParaView (Windows) with DFG 2D-3 tutorial](https://fenicsproject.discourse.group/t/adios2-bp-file-error-in-paraview-windows-with-dfg-2d-3-tutorial/17473)
**Author:** [@CFEnics](https://fenicsproject.discourse.group/u/CFEnics)\ **Replies:** 1\ **Last updated:** [April 24, 2025, 8:44pm UTC](https://fenicsproject.discourse.group/t/adios2-bp-file-error-in-paraview-windows-with-dfg-2d-3-tutorial/17473 "2025-04-24T20:44:10Z")
Hi, I’m running the Test problem 2: Flow past a cylinder (DFG 2D-3 benchmark) from the FEniCSx tutorials and writing output using VTXWriter in .bp format. At the final steps of the simulation, when trying to open the .… --- ## [Paraview does not work with VTXWriter on 3rd order elements](https://fenicsproject.discourse.group/t/paraview-does-not-work-with-vtxwriter-on-3rd-order-elements/17143)
**Author:** [@Ignatii](https://fenicsproject.discourse.group/u/Ignatii)\ **Replies:** 4\ **Last updated:** [March 29, 2025, 4:36pm UTC](https://fenicsproject.discourse.group/t/paraview-does-not-work-with-vtxwriter-on-3rd-order-elements/17143 "2025-03-29T16:36:35Z")
Dear Community, I had a problem when opening files saved with VTXWriter. The error occurred while working with elements of the 3rd order. When opening a .bp file and moving to the last frame paraview raises an error. Af… --- ## [Saving output at points selected by user when running the IPCS solver](https://fenicsproject.discourse.group/t/saving-output-at-points-selected-by-user-when-running-the-ipcs-solver/17190)
**Author:** [@fontsize](https://fenicsproject.discourse.group/u/fontsize)\ **Replies:** 2\ **Last updated:** [March 13, 2025, 3:24am UTC](https://fenicsproject.discourse.group/t/saving-output-at-points-selected-by-user-when-running-the-ipcs-solver/17190 "2025-03-13T03:24:43Z")
I’m running the code in jorgensd/dolfinx\_ipcs: Simple IPCS solver for dolfinx. I ran the code as follows: download the docker and git clone the repository; run python3 create\_and\_convert\_2D\_mesh.py in command line; ru… --- ## [Fail to read tagged facets from mesh generated with GMSH](https://fenicsproject.discourse.group/t/fail-to-read-tagged-facets-from-mesh-generated-with-gmsh/17082)
**Author:** [@mekong](https://fenicsproject.discourse.group/u/mekong)\ **Replies:** 4\ **Last updated:** [March 1, 2025, 2:31pm UTC](https://fenicsproject.discourse.group/t/fail-to-read-tagged-facets-from-mesh-generated-with-gmsh/17082 "2025-03-01T14:31:17Z")
Hello, I would like to generate a 2d mesh by using gmsh.model.occ but I am having some issues. I generate the mesh with import meshio import argparse import gmsh import warnings parser = argparse.ArgumentParser() pars… --- ## [How to read a parallelized mesh on different machine?](https://fenicsproject.discourse.group/t/how-to-read-a-parallelized-mesh-on-different-machine/17103)
**Author:** [@Loewenhuegel](https://fenicsproject.discourse.group/u/Loewenhuegel)\ **Replies:** 2\ **Last updated:** [March 1, 2025, 12:44am UTC](https://fenicsproject.discourse.group/t/how-to-read-a-parallelized-mesh-on-different-machine/17103 "2025-03-01T00:44:31Z")
I successfully ran a transient simulation using dolfinx and at every timestep saved some of the solution functions to a .bp directory using a VTXWriter object from dolfinx.io: VTXWriter(MPI.COMM\_WORLD, "out.bp", functio… --- ## [Newbie hoping for a toolchain that does not exist?](https://fenicsproject.discourse.group/t/newbie-hoping-for-a-toolchain-that-does-not-exist/17057)
**Author:** [@ormkotta](https://fenicsproject.discourse.group/u/ormkotta)\ **Replies:** 5\ **Last updated:** [February 24, 2025, 6:43pm UTC](https://fenicsproject.discourse.group/t/newbie-hoping-for-a-toolchain-that-does-not-exist/17057 "2025-02-24T18:43:11Z")
In my ignorant mind, the desired toolchain should work something like this: If necessary, generate 3D geometries in some CAD program. Create the mesh interactively with the gmsh GUI, including the naming/definition of … --- ## [Cell numbering: inconsistent gmsh \<=\> dolfinx numbering](https://fenicsproject.discourse.group/t/cell-numbering-inconsistent-gmsh-dolfinx-numbering/16810)
**Author:** [@pa-beaufort](https://fenicsproject.discourse.group/u/pa-beaufort)\ **Replies:** 9\ **Last updated:** [January 24, 2025, 9:43am UTC](https://fenicsproject.discourse.group/t/cell-numbering-inconsistent-gmsh-dolfinx-numbering/16810 "2025-01-24T09:43:57Z")
Hello, The cell numbering between gmsh elementTags and doflinx original\_cell\_indexis not consistent for the following with this mesh.msh: import dolfinx.io.gmshio import numpy as np from mpi4py import MPI from dolfinx … --- ## [Write and read function(t). Previous thead not completed](https://fenicsproject.discourse.group/t/write-and-read-function-t-previous-thead-not-completed/16696)
**Author:** [@FrancoisPage](https://fenicsproject.discourse.group/u/FrancoisPage)\ **Replies:** 0\ **Last updated:** [January 9, 2025, 9:53pm UTC](https://fenicsproject.discourse.group/t/write-and-read-function-t-previous-thead-not-completed/16696 "2025-01-09T21:53:42Z")
I want to make a similation so I’m dealing with a 3 dimensional Space, a 3 Dimensional function u-\>(x-\>,t) Where → is for vector notation. I have seen that it was an unsolved problem in other threads. 1. People didn’t… --- ## [Issues when saving the output as numpy format, 'petsc4py.PETSc.Vec' object is not callable](https://fenicsproject.discourse.group/t/issues-when-saving-the-output-as-numpy-format-petsc4py-petsc-vec-object-is-not-callable/16665)
**Author:** [@fontsize](https://fenicsproject.discourse.group/u/fontsize)\ **Replies:** 2\ **Last updated:** [January 3, 2025, 3:28pm UTC](https://fenicsproject.discourse.group/t/issues-when-saving-the-output-as-numpy-format-petsc4py-petsc-vec-object-is-not-callable/16665 "2025-01-03T15:28:55Z")
I’m running the code in jorgensd/dolfinx\_ipcs: Simple IPCS solver for dolfinx. I ran the code as follows: download the docker and git clone the repository; run python3 create\_and\_convert\_2D\_mesh.py in command line; ru… --- ## [Error exporting field to XDMF in DolfinX v0.9.0.post1](https://fenicsproject.discourse.group/t/error-exporting-field-to-xdmf-in-dolfinx-v0-9-0-post1/16641)
**Author:** [@MatsievskiySV](https://fenicsproject.discourse.group/u/MatsievskiySV)\ **Replies:** 3\ **Last updated:** [January 1, 2025, 8:41am UTC](https://fenicsproject.discourse.group/t/error-exporting-field-to-xdmf-in-dolfinx-v0-9-0-post1/16641 "2025-01-01T08:41:34Z")
The following program solves the Maxwell’s equations and stores fields to XDMF file. Paraview crashes when trying to open the result. Is it a bug, or did I do something wrong? This MWE is similar to Error exporting fiel… --- ## [Ideal workflow for saving parallel data?](https://fenicsproject.discourse.group/t/ideal-workflow-for-saving-parallel-data/16647)
**Author:** [@Chaitanya\_Apte](https://fenicsproject.discourse.group/u/Chaitanya_Apte)\ **Replies:** 0\ **Last updated:** [December 31, 2024, 7:35am UTC](https://fenicsproject.discourse.group/t/ideal-workflow-for-saving-parallel-data/16647 "2024-12-31T07:35:58Z")
In this example code, after solving parallelly I am plotting displacement field for a submesh. What is the best way to store the parallel mesh and solution so that I can get the required plots for any other submesh late… --- ## [In the thermal process, the temperature is going to less than the ambient as BC](https://fenicsproject.discourse.group/t/in-the-thermal-process-the-temperature-is-going-to-less-than-the-ambient-as-bc/16639)
**Author:** [@Mohamadrezash204](https://fenicsproject.discourse.group/u/Mohamadrezash204)\ **Replies:** 6\ **Last updated:** [December 30, 2024, 12:49pm UTC](https://fenicsproject.discourse.group/t/in-the-thermal-process-the-temperature-is-going-to-less-than-the-ambient-as-bc/16639 "2024-12-30T12:49:19Z")
ّn this code, I am getting the temperature less than ambient. Although the BC implant is seemingly correct. I can’t explain why it happens. can you help me? import fenics as fe import numpy as np def simulation(): … --- ## [Reading and writing meshtags on 2rd order mesh with adios4dolfinx](https://fenicsproject.discourse.group/t/reading-and-writing-meshtags-on-2rd-order-mesh-with-adios4dolfinx/16634)
**Author:** [@zsmb](https://fenicsproject.discourse.group/u/zsmb)\ **Replies:** 2\ **Last updated:** [December 27, 2024, 2:23am UTC](https://fenicsproject.discourse.group/t/reading-and-writing-meshtags-on-2rd-order-mesh-with-adios4dolfinx/16634 "2024-12-27T02:23:26Z")
I changed the mesh used here https://github.com/jorgensd/adios4dolfinx/blob/main/docs/meshtags.py from dolfinx buidin mesh to Gmsh mesh. Here is the code: import logging from pathlib import Path from mpi4py import MPI… --- ## [Plot mesh parallel, show partitioning](https://fenicsproject.discourse.group/t/plot-mesh-parallel-show-partitioning/16589)
**Author:** [@Stein](https://fenicsproject.discourse.group/u/Stein)\ **Replies:** 7\ **Last updated:** [December 25, 2024, 10:26am UTC](https://fenicsproject.discourse.group/t/plot-mesh-parallel-show-partitioning/16589 "2024-12-25T10:26:09Z")
I’d like to pyvista-plot my mesh, when running on multiple processors, with a flag for showing mesh partitioning or not (the ‘or not’ is where I struggle). I am following How to collect the global mesh without writing a… --- ## [How to export entity markers and nodal sources using io.XDMFFile](https://fenicsproject.discourse.group/t/how-to-export-entity-markers-and-nodal-sources-using-io-xdmffile/16248)
**Author:** [@alex24](https://fenicsproject.discourse.group/u/alex24)\ **Replies:** 1\ **Last updated:** [November 9, 2024, 7:20am UTC](https://fenicsproject.discourse.group/t/how-to-export-entity-markers-and-nodal-sources-using-io-xdmffile/16248 "2024-11-09T07:20:54Z")
Hi, Is there a way of writing the source vector (node loads in the code below) so they can be exported as an xdmf file and visualized in ParaView? How can bc facets (like boundary\_facets in the code below) be marked an… [Next page](https://fenicsproject.discourse.group/tag/io/3.md?match_all_tags=true&page=1&tags%5B%5D=io)