# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=4 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 5 --- ## [How to label the surfaces of a 3D mesh created in gmsh?](https://community.freefem.org/t/how-to-label-the-surfaces-of-a-3d-mesh-created-in-gmsh/4116)
**Author:** [@Ayataka](https://community.freefem.org/u/Ayataka)\ **Replies:** 0\ **Last updated:** [October 28, 2025, 1:22am UTC](https://community.freefem.org/t/how-to-label-the-surfaces-of-a-3d-mesh-created-in-gmsh/4116 "2025-10-28T01:22:34Z")
Hello, ff++ developers and users, I am currently seeking to perform structural analysis using a 3D mesh created in Gmsh. I am encountering difficulties as I am unable to label the surfaces that define the boundary cond… --- ## [Zoom Discussion / Session](https://community.freefem.org/t/zoom-discussion-session/2719)
**Author:** [@frederichecht](https://community.freefem.org/u/frederichecht)\ **Replies:** 12\ **Last updated:** [October 27, 2025, 8:20am UTC](https://community.freefem.org/t/zoom-discussion-session/2719 "2025-10-27T08:20:02Z")
Dear all, On first Wednesday for each month (with some exception) , I will open a zoom visio session od 2 hours form 10h to 12h (Paris time), to speak about FreeFEM++. Novelty, Futur, Problem, Bug,. Remark (it is a sh… --- ## [How to get Matrix^-1 \* Matrix in Schur-complement](https://community.freefem.org/t/how-to-get-matrix-1-matrix-in-schur-complement/4114)
**Author:** [@Guo.q.q](https://community.freefem.org/u/Guo.q.q)\ **Replies:** 3\ **Last updated:** [October 27, 2025, 5:16am UTC](https://community.freefem.org/t/how-to-get-matrix-1-matrix-in-schur-complement/4114 "2025-10-27T05:16:57Z")
Hello members and developers of the FreeFEM： While testing the Schur-complement method for solving a certain matrix(My thoughts are shown in the attachment), I noticed that FreeFEM++ does not support operations like Mat… --- ## [How to set AttachCoarseOperator?](https://community.freefem.org/t/how-to-set-attachcoarseoperator/4111)
**Author:** [@lzjqingao](https://community.freefem.org/u/lzjqingao)\ **Replies:** 9\ **Last updated:** [October 23, 2025, 3:12pm UTC](https://community.freefem.org/t/how-to-set-attachcoarseoperator/4111 "2025-10-23T15:12:35Z")
Hello, I am studying how to set the two-level GenEo algorithm by calling hpddm directly, and the code elasticity.edp in ~/examples/hpddm is related closely to my purpose. My problem is about the setting of AttachCoarseOp… --- ## [How to solve the 2D nonlinear problem having time-dependent BCs](https://community.freefem.org/t/how-to-solve-the-2d-nonlinear-problem-having-time-dependent-bcs/4110)
**Author:** [@M\_Usman](https://community.freefem.org/u/M_Usman)\ **Replies:** 0\ **Last updated:** [October 23, 2025, 9:50am UTC](https://community.freefem.org/t/how-to-solve-the-2d-nonlinear-problem-having-time-dependent-bcs/4110 "2025-10-23T09:50:51Z")
Hi, I hope everyone is doing well. I want to compute the numerical solution of the following problem which have time-dependent boundary conditions. --- ## [Mechanical behavior of contacts](https://community.freefem.org/t/mechanical-behavior-of-contacts/678)
**Author:** [@chaimaa](https://community.freefem.org/u/chaimaa)\ **Replies:** 2\ **Last updated:** [October 23, 2025, 1:46am UTC](https://community.freefem.org/t/mechanical-behavior-of-contacts/678 "2025-10-23T01:46:58Z")
Hello, Does anyone, know how to implement mechanical behavior of contacts. i want to know how to affect more than material to the components of the system. Thanks. --- ## [PETSc and Mesh interpolation](https://community.freefem.org/t/petsc-and-mesh-interpolation/4109)
**Author:** [@HMasson](https://community.freefem.org/u/HMasson)\ **Replies:** 3\ **Last updated:** [October 21, 2025, 1:35pm UTC](https://community.freefem.org/t/petsc-and-mesh-interpolation/4109 "2025-10-21T13:35:35Z")
Hello FreeFem community, I am trying to solve a 3D elastic problem using parallel computing with PETSc and multiple meshes. In my problem, I use 2 different meshes, one is an optimization domain (Inner mesh), and the s… --- ## [Object forwarded to DLL-plugin as by copy(clone) or reference?](https://community.freefem.org/t/object-forwarded-to-dll-plugin-as-by-copy-clone-or-reference/4108)
**Author:** [@MBK](https://community.freefem.org/u/MBK)\ **Replies:** 1\ **Last updated:** [October 20, 2025, 4:45pm UTC](https://community.freefem.org/t/object-forwarded-to-dll-plugin-as-by-copy-clone-or-reference/4108 "2025-10-20T16:45:42Z")
Hello! When I have an object in FreeFEM++ (like a vertex) from a mesh, and deliver or forward this (vertex-)object to my C++ DLL (plugin), is this forwarded by copy or by reference? Will the (vertex-)object only be a c… --- ## [Memory leak with tetgconvexhull](https://community.freefem.org/t/memory-leak-with-tetgconvexhull/4107)
**Author:** [@fb77](https://community.freefem.org/u/fb77)\ **Replies:** 2\ **Last updated:** [October 20, 2025, 1:36pm UTC](https://community.freefem.org/t/memory-leak-with-tetgconvexhull/4107 "2025-10-20T13:36:58Z")
It seems that there is a problem with tetgconvexhull, it generates the message ######## We forget of deleting 1 Nb pointer, 0Bytes , mpirank 0, memory leak =12320 CodeAlloc : nb ptr 4164, size :534928 mpirank: … --- ## [meshL (Line) with different colored dots in plot](https://community.freefem.org/t/meshl-line-with-different-colored-dots-in-plot/4106)
**Author:** [@MBK](https://community.freefem.org/u/MBK)\ **Replies:** 0\ **Last updated:** [October 20, 2025, 11:08am UTC](https://community.freefem.org/t/meshl-line-with-different-colored-dots-in-plot/4106 "2025-10-20T11:08:36Z")
Hello! When playing and testing with meshL I have sometimes red or black dots on the line in plot. What does that colored difference mean? Some kind of indicator for cleanness? Greetings --- ## [3D cube with 1D-Line in the middle](https://community.freefem.org/t/3d-cube-with-1d-line-in-the-middle/4104)
**Author:** [@MBK](https://community.freefem.org/u/MBK)\ **Replies:** 8\ **Last updated:** [October 20, 2025, 10:00am UTC](https://community.freefem.org/t/3d-cube-with-1d-line-in-the-middle/4104 "2025-10-20T10:00:22Z")
Hello! I want to create a 3D cube, with labeled line\* (or border) in the middle, where the tetraeders or tetrahedralization adapts or uses the vertexes of the 1D-line. Just a 3D cube with a labeled line in it as one mes… --- ## [Neumann boundary condition in 1D example](https://community.freefem.org/t/neumann-boundary-condition-in-1d-example/3137)
**Author:** [@MBK](https://community.freefem.org/u/MBK)\ **Replies:** 2\ **Last updated:** [October 17, 2025, 9:57pm UTC](https://community.freefem.org/t/neumann-boundary-condition-in-1d-example/3137 "2025-10-17T21:57:11Z")
Hi, how do I set a Neumann boundary condition in a 1D example in varf? With int0d? Greetings! --- ## [Dirichlet condition in 3D over a surface](https://community.freefem.org/t/dirichlet-condition-in-3d-over-a-surface/4089)
**Author:** [@Christophe](https://community.freefem.org/u/Christophe)\ **Replies:** 7\ **Last updated:** [October 17, 2025, 3:39pm UTC](https://community.freefem.org/t/dirichlet-condition-in-3d-over-a-surface/4089 "2025-10-17T15:39:36Z")
Hello everyone, I would like to impose a Dirichlet boundary condition over a surface in 3D. My geometry is simply a cylinder and the surface on which I would like to impose the Dirichlet condition is a disk. I used a 2… --- ## [Can we control the domain decomposition](https://community.freefem.org/t/can-we-control-the-domain-decomposition/4105)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 4\ **Last updated:** [October 17, 2025, 1:24pm UTC](https://community.freefem.org/t/can-we-control-the-domain-decomposition/4105 "2025-10-17T13:24:18Z")
Dear all, I have a question, that is can we control the domain decomposition by ourselves? For example, for a fluid-structure interaction(large fluid and small solid), if I have ten processors, I want to allocate one … --- ## [Zero pivot in LU factorization](https://community.freefem.org/t/zero-pivot-in-lu-factorization/4102)
**Author:** [@RNlao](https://community.freefem.org/u/RNlao)\ **Replies:** 3\ **Last updated:** [October 17, 2025, 9:25am UTC](https://community.freefem.org/t/zero-pivot-in-lu-factorization/4102 "2025-10-17T09:25:12Z")
Dear FreeFEM community, I‘m new to Freefem and I have been trying to conduct a resolvent analysis with incompressible flow. When I use the KSPSolve to get the inverse matrix, I met a problem \[0\]PETSC ERROR: Zero pivot … --- ## [Composite finite element spaces with SLEPc](https://community.freefem.org/t/composite-finite-element-spaces-with-slepc/4000)
**Author:** [@quentin](https://community.freefem.org/u/quentin)\ **Replies:** 16\ **Last updated:** [October 15, 2025, 3:33pm UTC](https://community.freefem.org/t/composite-finite-element-spaces-with-slepc/4000 "2025-10-15T15:33:08Z")
Dear FreeFEM community, I have been trying the new feature composite finite element space, which seems quite powerful. However, when I attempted use a composite FE space together with EPSSolve, a problem arose: how to c… --- ## [How to impose interface condition ∂u⁺/∂n = k ∂u⁻/∂n in FreeFem++](https://community.freefem.org/t/how-to-impose-interface-condition-u-n-k-u-n-in-freefem/4084)
**Author:** [@Kamjd](https://community.freefem.org/u/Kamjd)\ **Replies:** 4\ **Last updated:** [October 13, 2025, 2:46am UTC](https://community.freefem.org/t/how-to-impose-interface-condition-u-n-k-u-n-in-freefem/4084 "2025-10-13T02:46:39Z")
Hello everyone, I am solving a PDE on a domain Ω split into two sub-domains Ω⁺ and Ω⁻ separated by an interface Γ. On Γ I need to impose the interface (flux) condition \[ \\frac{\\partial u^{+}}{\\partial n} = k,\\frac{\\p… --- ## [About solve matrix](https://community.freefem.org/t/about-solve-matrix/4098)
**Author:** [@qingYang](https://community.freefem.org/u/qingYang)\ **Replies:** 3\ **Last updated:** [October 10, 2025, 12:57pm UTC](https://community.freefem.org/t/about-solve-matrix/4098 "2025-10-10T12:57:46Z")
Dear FreeFem developers and users: I would like to ask a question and hope to receive some help or suggestions. (1)Background: For the following global matrix KGlobal (where A, B, C, etc., are all block matrices), it i… --- ## [About mesh region and label](https://community.freefem.org/t/about-mesh-region-and-label/2840)
**Author:** [@qingYang](https://community.freefem.org/u/qingYang)\ **Replies:** 3\ **Last updated:** [October 10, 2025, 12:32am UTC](https://community.freefem.org/t/about-mesh-region-and-label/2840 "2025-10-10T00:32:18Z")
Hello everyone, I extracted a certain face from the externally imported mesh as a 2D mesh (Th), but after extraction, all regions and labels in Th are 0 (as shown in the figure). I want to know how to assign regions and … --- ## [Syntax question](https://community.freefem.org/t/syntax-question/4093)
**Author:** [@pnegron](https://community.freefem.org/u/pnegron)\ **Replies:** 3\ **Last updated:** [October 8, 2025, 1:43pm UTC](https://community.freefem.org/t/syntax-question/4093 "2025-10-08T13:43:03Z")
What is the difference between the following code (please note the use of brackets in the P1): mesh Th=square(10,10); fespace Wh(Th,\[P1\]); and mesh Th=square(10,10); fespace Wh(Th,P1); Thanks you! P. Negron. --- ## [Rate fo convergence for fourth-order variational inequality](https://community.freefem.org/t/rate-fo-convergence-for-fourth-order-variational-inequality/4097)
**Author:** [@smail](https://community.freefem.org/u/smail)\ **Replies:** 0\ **Last updated:** [October 8, 2025, 7:28am UTC](https://community.freefem.org/t/rate-fo-convergence-for-fourth-order-variational-inequality/4097 "2025-10-08T07:28:52Z")
Hi, I’m trying to compute the order of convergence for a fourth-order variational inequality using the penalty method, in FreeFEM++. But I got unexpected results. I computed the L2 and the H1 errors against an exact s… --- ## [Evaluating Solution at Arbitrary Points](https://community.freefem.org/t/evaluating-solution-at-arbitrary-points/4028)
**Author:** [@wdachub](https://community.freefem.org/u/wdachub)\ **Replies:** 4\ **Last updated:** [October 7, 2025, 12:02am UTC](https://community.freefem.org/t/evaluating-solution-at-arbitrary-points/4028 "2025-10-07T00:02:26Z")
Dear FreeFEM users and developers, I am trying to evaluate the value of a solution at a specific point in order to compare it with a theoretical value. If the point lies exactly on a mesh node, the method described in t… --- ## [Load Error PETSc Complex (v4.14)](https://community.freefem.org/t/load-error-petsc-complex-v4-14/3080)
**Author:** [@RaMattoso](https://community.freefem.org/u/RaMattoso)\ **Replies:** 4\ **Last updated:** [October 6, 2025, 11:39pm UTC](https://community.freefem.org/t/load-error-petsc-complex-v4-14/3080 "2025-10-06T23:39:33Z")
Hello everyone! I use Windows and had to format my machine. I don’t remember which version of FF++ I was using before, but I installed the current version available, v4.14, and I can’t run my code. The error is as fol… --- ## [3D breast mesh from an image](https://community.freefem.org/t/3d-breast-mesh-from-an-image/4080)
**Author:** [@lassounon](https://community.freefem.org/u/lassounon)\ **Replies:** 3\ **Last updated:** [October 6, 2025, 7:45am UTC](https://community.freefem.org/t/3d-breast-mesh-from-an-image/4080 "2025-10-06T07:45:56Z")
Hello everyone, I’m trying to create a 3D breast mesh from an image, just as I would with a 2D mesh. But it doesn’t work. I looked at the 3d-Leman example, but which isn’t generated directly from an image. Please help m… --- ## [3D Rotating Hill problem](https://community.freefem.org/t/3d-rotating-hill-problem/4092)
**Author:** [@ZZM](https://community.freefem.org/u/ZZM)\ **Replies:** 4\ **Last updated:** [October 6, 2025, 12:42am UTC](https://community.freefem.org/t/3d-rotating-hill-problem/4092 "2025-10-06T00:42:03Z")
I want to use the DG to solve the Rotating Hill. In 2D, I can ues the nTonEdge, So How about in 3D --- ## [Discontinuous fields](https://community.freefem.org/t/discontinuous-fields/4081)
**Author:** [@msamani](https://community.freefem.org/u/msamani)\ **Replies:** 4\ **Last updated:** [October 3, 2025, 9:46am UTC](https://community.freefem.org/t/discontinuous-fields/4081 "2025-10-03T09:46:33Z")
I am trying model heat in an assembly with interfaces between different materials at low temperatures. This implies the existence of Kapitza resistance only at those interfaces (so Discontinuous Gelarkin is probably not … --- ## [Navier Stokes with very small time steps](https://community.freefem.org/t/navier-stokes-with-very-small-time-steps/4082)
**Author:** [@Arun](https://community.freefem.org/u/Arun)\ **Replies:** 1\ **Last updated:** [October 3, 2025, 9:34am UTC](https://community.freefem.org/t/navier-stokes-with-very-small-time-steps/4082 "2025-10-03T09:34:52Z")
Hello, I am trying to solve incompressible transient Navier Stokes equation using very small time steps. I have tried the examples given in the documentation including the projection and NS Uzawa Cahouet Chabart solvers… --- ## [Fracture network in FreeFEM](https://community.freefem.org/t/fracture-network-in-freefem/4090)
**Author:** [@Hemanta822](https://community.freefem.org/u/Hemanta822)\ **Replies:** 0\ **Last updated:** [September 30, 2025, 11:03pm UTC](https://community.freefem.org/t/fracture-network-in-freefem/4090 "2025-09-30T23:03:47Z")
Dear All, Is there any way to create fracture network like the following in FreeFEM? I could only create 3-4 of the making rectangles of very small width. I would greatly appriciate your suggestion. Thank you. --- ## [Saving Data from Electromagnetism Simulation with Nedelec Edge Elements](https://community.freefem.org/t/saving-data-from-electromagnetism-simulation-with-nedelec-edge-elements/4083)
**Author:** [@Box](https://community.freefem.org/u/Box)\ **Replies:** 2\ **Last updated:** [September 29, 2025, 2:58pm UTC](https://community.freefem.org/t/saving-data-from-electromagnetism-simulation-with-nedelec-edge-elements/4083 "2025-09-29T14:58:02Z")
ubject: Saving Data from Electromagnetism Simulation with Nedelec Edge Elements Good afternoon everyone, I’m writing because I’m trying to save data after running an electromagnetism simulation based on Nedelec Edge el… --- ## [Compressible turbulent Navier–Stokes around a sphere (half-sphere, cylindrical coordinates) — strange field despite BCs implemented](https://community.freefem.org/t/compressible-turbulent-navier-stokes-around-a-sphere-half-sphere-cylindrical-coordinates-strange-field-despite-bcs-implemented/4079)
**Author:** [@ipnglt](https://community.freefem.org/u/ipnglt)\ **Replies:** 6\ **Last updated:** [September 26, 2025, 1:44pm UTC](https://community.freefem.org/t/compressible-turbulent-navier-stokes-around-a-sphere-half-sphere-cylindrical-coordinates-strange-field-despite-bcs-implemented/4079 "2025-09-26T13:44:13Z")
Dear all, I am trying to solve the compressible, turbulent Navier–Stokes equations for a simple test case: flow around a sphere. To exploit symmetry I model half the sphere in cylindrical coordinates. I use FreeFem++ fo… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=3) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=5)