# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=8 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 9 --- ## [Parallelize Navier Stokes with moving boundary](https://community.freefem.org/t/parallelize-navier-stokes-with-moving-boundary/3904)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 12\ **Last updated:** [May 11, 2025, 5:07am UTC](https://community.freefem.org/t/parallelize-navier-stokes-with-moving-boundary/3904 "2025-05-11T05:07:40Z")
Dear all, I already implement the sequential version of NS equation with moving boundary in FreeFem++, the code is sequential\_moving\_boundary.edp (2.4 KB) Now I want to parallelize it using PETSc, just change little, … --- ## [Discontinuous Galerkin Stokes Problem](https://community.freefem.org/t/discontinuous-galerkin-stokes-problem/3082)
**Author:** [@Aubium](https://community.freefem.org/u/Aubium)\ **Replies:** 3\ **Last updated:** [May 10, 2025, 9:29am UTC](https://community.freefem.org/t/discontinuous-galerkin-stokes-problem/3082 "2025-05-10T09:29:02Z")
Good evening members, I’m struggling with the implementation of an incompressible Stokes equation using Disontinuous Galerkin method. Here are my questions : How to write the integral on border edges ? How to write th… --- ## [The nonlinear term of Navier-Stokes by DG method](https://community.freefem.org/t/the-nonlinear-term-of-navier-stokes-by-dg-method/3908)
**Author:** [@LXX](https://community.freefem.org/u/LXX)\ **Replies:** 0\ **Last updated:** [May 10, 2025, 9:09am UTC](https://community.freefem.org/t/the-nonlinear-term-of-navier-stokes-by-dg-method/3908 "2025-05-10T09:09:36Z")
Hello, everyone. Right now I’m trying to write DG code using FreeFem++, but when calculating the boundary integrals on the nonlinear terms of the navier-stokes equation, I’m running into problems that I can’t represen… --- ## [Trying to solve 1D wave equation but not getting the plot correct](https://community.freefem.org/t/trying-to-solve-1d-wave-equation-but-not-getting-the-plot-correct/3905)
**Author:** [@ds2201](https://community.freefem.org/u/ds2201)\ **Replies:** 4\ **Last updated:** [May 9, 2025, 7:49am UTC](https://community.freefem.org/t/trying-to-solve-1d-wave-equation-but-not-getting-the-plot-correct/3905 "2025-05-09T07:49:05Z")
I am trying to solve the 1D wave equation. When I am trying to plot the approximated solution I am getting a straight line. Can anyone please check what is wrong with the plot command. As I am unable to attach the edp f… --- ## ["Ambiguity polymorfic" error in Maxwell equation with PML](https://community.freefem.org/t/ambiguity-polymorfic-error-in-maxwell-equation-with-pml/2619)
**Author:** [@RaMattoso](https://community.freefem.org/u/RaMattoso)\ **Replies:** 2\ **Last updated:** [May 7, 2025, 12:04am UTC](https://community.freefem.org/t/ambiguity-polymorfic-error-in-maxwell-equation-with-pml/2619 "2025-05-07T00:04:15Z")
Dear fellows, I’m trying to code an electromagnetism problem using Maxwell equation in variational form (Scaterring problem) and Perfectly Matched Layer - PML (as boundary condition). Because PML is present, I have to s… --- ## [What's wrong with my code](https://community.freefem.org/t/whats-wrong-with-my-code/3902)
**Author:** [@BelfaidaMedReda](https://community.freefem.org/u/BelfaidaMedReda)\ **Replies:** 2\ **Last updated:** [May 6, 2025, 1:14pm UTC](https://community.freefem.org/t/whats-wrong-with-my-code/3902 "2025-05-06T13:14:31Z")
Hello, I’m new to freefem, I can’t compute the eigenvalues as I’m getting this error 71 : varf a(u, v) = int2d(T)( dx(u) unknown operator ( on type Error line number 71, in file drum\_shapestest.edp, before token ) c… --- ## [Issue with movemesh and Grid Spacing in 1D Domain with Material Removal](https://community.freefem.org/t/issue-with-movemesh-and-grid-spacing-in-1d-domain-with-material-removal/3901)
**Author:** [@goutham2023](https://community.freefem.org/u/goutham2023)\ **Replies:** 0\ **Last updated:** [May 6, 2025, 6:37am UTC](https://community.freefem.org/t/issue-with-movemesh-and-grid-spacing-in-1d-domain-with-material-removal/3901 "2025-05-06T06:37:21Z")
Hello FreeFem community, I’m working on a 1D simulation involving material removal over time. I’m using the movemesh command to update the domain dimensions. However, after interpolation, I noticed that the grid spacing… --- ## [DG for Steady Stokes](https://community.freefem.org/t/dg-for-steady-stokes/3900)
**Author:** [@weixj](https://community.freefem.org/u/weixj)\ **Replies:** 0\ **Last updated:** [May 6, 2025, 4:14am UTC](https://community.freefem.org/t/dg-for-steady-stokes/3900 "2025-05-06T04:14:27Z")
I am trying to solve the stabilized stokes equation using the DG method with P2dc-P1dc elements to give an exact solution and verify the order of spatial convergence. This is my code, and the code run shows that the conv… --- ## [Questions of mapu and mapt](https://community.freefem.org/t/questions-of-mapu-and-mapt/3899)
**Author:** [@pi.3.141](https://community.freefem.org/u/pi.3.141)\ **Replies:** 0\ **Last updated:** [May 5, 2025, 2:39pm UTC](https://community.freefem.org/t/questions-of-mapu-and-mapt/3899 "2025-05-05T14:39:46Z")
Dear Freefemers, I am trying to understand the use of mapu and mapt features. I follow a few examples from the forum, but the results I obtain are not great. I have attached a piece of code, demonstrating how I use ma… --- ## [User defined function; pass fe or mesh arguments?](https://community.freefem.org/t/user-defined-function-pass-fe-or-mesh-arguments/3897)
**Author:** [@pi.3.141](https://community.freefem.org/u/pi.3.141)\ **Replies:** 2\ **Last updated:** [May 5, 2025, 2:07pm UTC](https://community.freefem.org/t/user-defined-function-pass-fe-or-mesh-arguments/3897 "2025-05-05T14:07:13Z")
Hello Freefem community, I wonder if it is possible to pass to user defined functions a finite element or mesh argument. For example, would it be possible something like below? Thank you! mesh Th=square(10,10) fespa… --- ## [Why '-pc\_type hypre' does not converge?](https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 2\ **Last updated:** [May 5, 2025, 1:34pm UTC](https://community.freefem.org/t/why-pc-type-hypre-does-not-converge/3898 "2025-05-05T13:34:20Z")
Dear all, When I parallelize my code of a 2D lid driven cavity problem. I found that when I choose set(NS, sparams = “-pc\_type lu”) the result is good. But when I choose to use set(NS, sparams = “-pc\_type hypre”, the re… --- ## [Variational formulation in cylindrical co ordinates](https://community.freefem.org/t/variational-formulation-in-cylindrical-co-ordinates/3891)
**Author:** [@sumenchalla](https://community.freefem.org/u/sumenchalla)\ **Replies:** 4\ **Last updated:** [May 2, 2025, 3:06pm UTC](https://community.freefem.org/t/variational-formulation-in-cylindrical-co-ordinates/3891 "2025-05-02T15:06:20Z")
Dear professor, I want to simulate the flow throught pipe using full 3D NS equations. I wanted to write the varional formulation in cylindrical coordinates. I was able to map ‘r’ coordinates with y and ‘z’ coordinates w… --- ## [La matrice de raideur lorsque la solution est un champ vectoriel](https://community.freefem.org/t/la-matrice-de-raideur-lorsque-la-solution-est-un-champ-vectoriel/3884)
**Author:** [@redaAkhdi](https://community.freefem.org/u/redaAkhdi)\ **Replies:** 6\ **Last updated:** [May 1, 2025, 2:39pm UTC](https://community.freefem.org/t/la-matrice-de-raideur-lorsque-la-solution-est-un-champ-vectoriel/3884 "2025-05-01T14:39:51Z")
comment recuperer la matrice de raideur lorsque la solution est un champ vectoriel ? voila mon code que je developpe // Définir la forme variationnelle pour la matrice de raideur varf a(\[u, v\], \[w, s\]) = int2d(th)( l… --- ## [Graded mesh in FreeFem++](https://community.freefem.org/t/graded-mesh-in-freefem/3894)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [April 30, 2025, 6:33pm UTC](https://community.freefem.org/t/graded-mesh-in-freefem/3894 "2025-04-30T18:33:42Z")
Dear all, Can graded mesh be created in FreeFem++??. I need it FreeFem++ code. I have to create it like in the following image: Here is the mcov: Thanks in advance!. --- ## [Request for Reproduction Setup of Cobra Cavity Example on 6144 Cores (198 Million DoFs)](https://community.freefem.org/t/request-for-reproduction-setup-of-cobra-cavity-example-on-6144-cores-198-million-dofs/3882)
**Author:** [@dhl2011dj](https://community.freefem.org/u/dhl2011dj)\ **Replies:** 1\ **Last updated:** [April 30, 2025, 10:25am UTC](https://community.freefem.org/t/request-for-reproduction-setup-of-cobra-cavity-example-on-6144-cores-198-million-dofs/3882 "2025-04-30T10:25:30Z")
Hello everyone, I am currently trying to reproduce the large-scale electromagnetic scattering simulation from the Cobra Cavity example shown on the FreeFEM gallery (https://freefem.org/gallery/cobra), where the problem … --- ## [Buffer overflow error with parmmg](https://community.freefem.org/t/buffer-overflow-error-with-parmmg/3890)
**Author:** [@GiacomoSperoni97](https://community.freefem.org/u/GiacomoSperoni97)\ **Replies:** 1\ **Last updated:** [April 29, 2025, 3:37pm UTC](https://community.freefem.org/t/buffer-overflow-error-with-parmmg/3890 "2025-04-29T15:37:28Z")
Dear community, I am trying a simple test for the parallel version of mesh adaptation using parmmg, but I encountered an unexpected buffer overflow error. Here is the code (taken from the example provided): // Run wit… --- ## [Importing data from file](https://community.freefem.org/t/importing-data-from-file/3859)
**Author:** [@mattiamurachelli](https://community.freefem.org/u/mattiamurachelli)\ **Replies:** 3\ **Last updated:** [April 29, 2025, 9:30am UTC](https://community.freefem.org/t/importing-data-from-file/3859 "2025-04-29T09:30:45Z")
Good evening, I was wondering if there was a way to import parameters from file in FreeFem++, for example in the way JSON does. I am aware of the existence of the getARGV() method but I was hoping for something more pra… --- ## [Can we use nonuniform time steps to compute Caputo Fractional derivative in Heat equation FF++ code? (My code is runing but not good result comes)](https://community.freefem.org/t/can-we-use-nonuniform-time-steps-to-compute-caputo-fractional-derivative-in-heat-equation-ff-code-my-code-is-runing-but-not-good-result-comes/3887)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [April 28, 2025, 3:44am UTC](https://community.freefem.org/t/can-we-use-nonuniform-time-steps-to-compute-caputo-fractional-derivative-in-heat-equation-ff-code-my-code-is-runing-but-not-good-result-comes/3887 "2025-04-28T03:44:33Z")
Dear all, i want to know that can we use nonuniform time steps in FreeFem++ to compute the following Caputo derivative for the fractional dervative in FreeFem++ ?? What will its Codes format??. I have tried like th… --- ## [Boundary condition in periodic mesh](https://community.freefem.org/t/boundary-condition-in-periodic-mesh/3880)
**Author:** [@taha](https://community.freefem.org/u/taha)\ **Replies:** 2\ **Last updated:** [April 24, 2025, 1:05pm UTC](https://community.freefem.org/t/boundary-condition-in-periodic-mesh/3880 "2025-04-24T13:05:04Z")
hello everyone, i have juste i small probleme about defining a dirichlet contion in down (y=-1)and up boundary (y=-1 +ny\*L) for the hall domain, it’s a porous media problem and i try to represent the solution in MACRO sc… --- ## [Trouble updating from 4.9 to 4.15](https://community.freefem.org/t/trouble-updating-from-4-9-to-4-15/3877)
**Author:** [@bpabbott](https://community.freefem.org/u/bpabbott)\ **Replies:** 2\ **Last updated:** [April 23, 2025, 6:39am UTC](https://community.freefem.org/t/trouble-updating-from-4-9-to-4-15/3877 "2025-04-23T06:39:56Z")
I’m quite novice at FreeFEM. I’ve been using edp-files we put together several years back (v9). While upgrading the a new computer I discovered that one of the edp-files throws an error in v15. I’ve included some of the … --- ## [Issues with coupled 1D-ODE](https://community.freefem.org/t/issues-with-coupled-1d-ode/3872)
**Author:** [@erigae](https://community.freefem.org/u/erigae)\ **Replies:** 11\ **Last updated:** [April 22, 2025, 6:30pm UTC](https://community.freefem.org/t/issues-with-coupled-1d-ode/3872 "2025-04-22T18:30:20Z")
Hi there, I’m rather new with FreeFEM and I’m trying to solve a simple 1D-ODE (2nd-order) with boundary conditions on the same (leftmost) boundary. Since it is not possible in the weak formulation to impose Dirichlet- … --- ## [Quadrilateral/Hex elements](https://community.freefem.org/t/quadrilateral-hex-elements/635)
**Author:** [@rahavven](https://community.freefem.org/u/rahavven)\ **Replies:** 4\ **Last updated:** [April 22, 2025, 11:52am UTC](https://community.freefem.org/t/quadrilateral-hex-elements/635 "2025-04-22T11:52:20Z")
Hello everyone, I am a new user of FreeFem++. Going through the documentation, I observe that at the moment only Triangular/Tetrahedral elements are supported. However, I would like to work with Quadrilateral/Hex elemen… --- ## [Average condition for pressur in stokes equation](https://community.freefem.org/t/average-condition-for-pressur-in-stokes-equation/3870)
**Author:** [@taha](https://community.freefem.org/u/taha)\ **Replies:** 4\ **Last updated:** [April 21, 2025, 8:03pm UTC](https://community.freefem.org/t/average-condition-for-pressur-in-stokes-equation/3870 "2025-04-21T20:03:19Z")
Hello everyone,i have a small question is it possible to add a condition that says the average of pressure that we want to calculate should equal to 0 ,here is my code that calculate the stokes equation in porous medium … --- ## [Navier Stokes on a step](https://community.freefem.org/t/navier-stokes-on-a-step/3861)
**Author:** [@lipesantosa](https://community.freefem.org/u/lipesantosa)\ **Replies:** 4\ **Last updated:** [April 21, 2025, 2:12pm UTC](https://community.freefem.org/t/navier-stokes-on-a-step/3861 "2025-04-21T14:12:44Z")
Hey, everyone! I’m still a problem with solve Navier Stokes equation on a step. When I plot, the vector come out of the mesh (what should not happen). Could someone help me? (It stays like this) Note: I’m using Newt… --- ## [Divergence of free surface in a liquid film problem](https://community.freefem.org/t/divergence-of-free-surface-in-a-liquid-film-problem/3873)
**Author:** [@quentin](https://community.freefem.org/u/quentin)\ **Replies:** 1\ **Last updated:** [April 21, 2025, 11:19am UTC](https://community.freefem.org/t/divergence-of-free-surface-in-a-liquid-film-problem/3873 "2025-04-21T11:19:25Z")
These days I’ve done a code to simulate a liquid film with a periodic free surface. After some steps, instability is observed on the upstream of the peak on the free surface. And it will evolution until the blowing up o… --- ## [Complex eigenvalues and eigenvectors of a real problem](https://community.freefem.org/t/complex-eigenvalues-and-eigenvectors-of-a-real-problem/3843)
**Author:** [@aszaboa](https://community.freefem.org/u/aszaboa)\ **Replies:** 10\ **Last updated:** [April 18, 2025, 3:42pm UTC](https://community.freefem.org/t/complex-eigenvalues-and-eigenvectors-of-a-real-problem/3843 "2025-04-18T15:42:13Z")
Hello everyone, I am trying to solve an eigenvalue problem in which the matricx is real, but I expect complex eigenvalues. When I run PETSc with real, I see in the convergence history that SLEPc indeed calculates real e… --- ## [Mesh based on breast image using P2 finite elements](https://community.freefem.org/t/mesh-based-on-breast-image-using-p2-finite-elements/3862)
**Author:** [@lassounon](https://community.freefem.org/u/lassounon)\ **Replies:** 3\ **Last updated:** [April 18, 2025, 11:03am UTC](https://community.freefem.org/t/mesh-based-on-breast-image-using-p2-finite-elements/3862 "2025-04-18T11:03:00Z")
Hello everyone. I used the image-based mesh generation code (Lemanlake example in the Freefem documentation, p. 194) to generate a breast mesh using P1 finite elements. I want the same thing with P2 finite elements. How… --- ## [Seeking Guidance on Debugging FreeFEM++](https://community.freefem.org/t/seeking-guidance-on-debugging-freefem/3869)
**Author:** [@MariamiMamgo](https://community.freefem.org/u/MariamiMamgo)\ **Replies:** 0\ **Last updated:** [April 17, 2025, 8:39pm UTC](https://community.freefem.org/t/seeking-guidance-on-debugging-freefem/3869 "2025-04-17T20:39:23Z")
Hello, I’ve recently installed FreeFEM++ source code on my Windows machine by following the instructions provided on the website. I’ve successfully configured, built, and run the FreeFEM++ code. However, I’d like to und… --- ## [Plot part of 3D](https://community.freefem.org/t/plot-part-of-3d/3863)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 5\ **Last updated:** [April 17, 2025, 5:40pm UTC](https://community.freefem.org/t/plot-part-of-3d/3863 "2025-04-17T17:40:18Z")
Can freefem++ plot one labelled surface of a 3D geometry? --- ## [Polygonal Mesh in FreeFEM++](https://community.freefem.org/t/polygonal-mesh-in-freefem/3868)
**Author:** [@kallol](https://community.freefem.org/u/kallol)\ **Replies:** 1\ **Last updated:** [April 17, 2025, 12:10pm UTC](https://community.freefem.org/t/polygonal-mesh-in-freefem/3868 "2025-04-17T12:10:02Z")
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