# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=7 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 8 --- ## [Mesh, regions and numbering](https://community.freefem.org/t/mesh-regions-and-numbering/3961)
**Author:** [@pi.3.141](https://community.freefem.org/u/pi.3.141)\ **Replies:** 1\ **Last updated:** [June 8, 2025, 2:52am UTC](https://community.freefem.org/t/mesh-regions-and-numbering/3961 "2025-06-08T02:52:30Z")
Hello, I have a problem with two meshes, say Th1 and Th2, with Th1 extracted from Th2 (Th1 subset of Th2). I have to integrate in Th1 a product u1\*u2, with u1 in Th1, u2 in Th2, and u1 and u2 say of class P1. I prefer … --- ## [Solving flow in a periodic cell and extending to full domain](https://community.freefem.org/t/solving-flow-in-a-periodic-cell-and-extending-to-full-domain/3959)
**Author:** [@wdachub](https://community.freefem.org/u/wdachub)\ **Replies:** 0\ **Last updated:** [June 6, 2025, 3:59am UTC](https://community.freefem.org/t/solving-flow-in-a-periodic-cell-and-extending-to-full-domain/3959 "2025-06-06T03:59:11Z")
I’m working with a channel geometry that has periodic variations. My goal is to solve the Navier–Stokes equations to compute the velocity field, and then use this field to advect a passive scalar. Currently, I compute t… --- ## [dG code for periodic boundary condition](https://community.freefem.org/t/dg-code-for-periodic-boundary-condition/3820)
**Author:** [@pratyay](https://community.freefem.org/u/pratyay)\ **Replies:** 7\ **Last updated:** [June 4, 2025, 10:13am UTC](https://community.freefem.org/t/dg-code-for-periodic-boundary-condition/3820 "2025-06-04T10:13:13Z")
Can I run a discontinous galerkin code for periodic boundary conditions in free fem ++? Which version is good for this? --- ## [Rectangular non-uniform mesh](https://community.freefem.org/t/rectangular-non-uniform-mesh/3874)
**Author:** [@Suraj\_k\_11](https://community.freefem.org/u/Suraj_k_11)\ **Replies:** 7\ **Last updated:** [May 31, 2025, 11:52am UTC](https://community.freefem.org/t/rectangular-non-uniform-mesh/3874 "2025-05-31T11:52:08Z")
Can we use rectangular non uniform mesh in free fem++? --- ## [Need help to create quadrilateral mesh in FreeFem++ in 2D](https://community.freefem.org/t/need-help-to-create-quadrilateral-mesh-in-freefem-in-2d/3952)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [May 30, 2025, 7:54pm UTC](https://community.freefem.org/t/need-help-to-create-quadrilateral-mesh-in-freefem-in-2d/3952 "2025-05-30T19:54:01Z")
Hello everyone, I would like to create a quadrilateral mesh in FreeFem++ without any triangular elements. Could you please help me?. Thanks in advance!. --- ## [What does 20 in convectParallel(Mesh, \[u1, u2\], -dt, c, 20) mean](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 5\ **Last updated:** [May 30, 2025, 8:42am UTC](https://community.freefem.org/t/what-does-20-in-convectparallel-mesh-u1-u2-dt-c-20-mean/3931 "2025-05-30T08:42:03Z")
Does anyone know what 20 denotes in command convectParallel(Mesh, \[u1, u2\], -dt, c, 20) ? --- ## [DG method with periodic boundary condition](https://community.freefem.org/t/dg-method-with-periodic-boundary-condition/3943)
**Author:** [@kail](https://community.freefem.org/u/kail)\ **Replies:** 17\ **Last updated:** [May 30, 2025, 4:33am UTC](https://community.freefem.org/t/dg-method-with-periodic-boundary-condition/3943 "2025-05-30T04:33:04Z")
I don’t know how to deal with the periodic bcd in DG method. I have successfully finished the Dirichlet or Nuemann bcd for Poisson equation with DG method. I set the left and right bcd is periodic, and the main difficu… --- ## [Order of variables in matrix generated with varf with a \[P1, P1, P0\] fespace](https://community.freefem.org/t/order-of-variables-in-matrix-generated-with-varf-with-a-p1-p1-p0-fespace/3489)
**Author:** [@djahid](https://community.freefem.org/u/djahid)\ **Replies:** 5\ **Last updated:** [May 29, 2025, 2:28pm UTC](https://community.freefem.org/t/order-of-variables-in-matrix-generated-with-varf-with-a-p1-p1-p0-fespace/3489 "2025-05-29T14:28:15Z")
Hello, I’m trying to compare the matrix generated from the following code with another code I have that solves the same problem mesh Th=square(2, 2); fespace Xh(Th,P1); fespace Mh(Th,P0); fespace XhxXhxMh(Th,\[P1,P1,P0\]… --- ## [Coupling a systeme of equation](https://community.freefem.org/t/coupling-a-systeme-of-equation/3945)
**Author:** [@taha](https://community.freefem.org/u/taha)\ **Replies:** 6\ **Last updated:** [May 28, 2025, 12:48pm UTC](https://community.freefem.org/t/coupling-a-systeme-of-equation/3945 "2025-05-28T12:48:14Z")
Hello everyone,i’m just trying to couple this three equations,but i get false relsuts,i coupled the systeme by giving an arbitrary value of T,then solving the first equation then the third and then the second,and i ke… --- ## [Time-harmonic, birefringent Maxwell for 3D anisotropic medium with phase shifting light](https://community.freefem.org/t/time-harmonic-birefringent-maxwell-for-3d-anisotropic-medium-with-phase-shifting-light/3939)
**Author:** [@wurschtbrotwilli](https://community.freefem.org/u/wurschtbrotwilli)\ **Replies:** 1\ **Last updated:** [May 28, 2025, 5:54am UTC](https://community.freefem.org/t/time-harmonic-birefringent-maxwell-for-3d-anisotropic-medium-with-phase-shifting-light/3939 "2025-05-28T05:54:18Z")
Hello everyone, I need some guidance on how to achieve proper results with this simulation. I want to simulate the light propagation through a medium with an inclusion. I assume sourceless, non-magnetic, time-harmonic c… --- ## [Buildmesh from meshL with a hole](https://community.freefem.org/t/buildmesh-from-meshl-with-a-hole/3938)
**Author:** [@Loic](https://community.freefem.org/u/Loic)\ **Replies:** 1\ **Last updated:** [May 26, 2025, 2:15pm UTC](https://community.freefem.org/t/buildmesh-from-meshl-with-a-hole/3938 "2025-05-26T14:15:56Z")
Dear all, I would like to reconstruct a 2D from a meshL obtained with extract(). TO illustrate my problems I give a small example. I have a 2D mesh of a square with a hole (ThBinder) I have a 2D mesh of a sphere (T… --- ## [Not getting accurate order of convergence](https://community.freefem.org/t/not-getting-accurate-order-of-convergence/3928)
**Author:** [@xavier1](https://community.freefem.org/u/xavier1)\ **Replies:** 16\ **Last updated:** [May 26, 2025, 11:02am UTC](https://community.freefem.org/t/not-getting-accurate-order-of-convergence/3928 "2025-05-26T11:02:40Z")
I compute the solution for several spatial mesh sizes and measure the L2 error with respect to the exact solution. My goal is to study the order of convergence, but the computed rates seem inconsistent or lower than expe… --- ## [Coupling three equations for a homogenization problem with the Boussinesq approximation](https://community.freefem.org/t/coupling-three-equations-for-a-homogenization-problem-with-the-boussinesq-approximation/3936)
**Author:** [@taha](https://community.freefem.org/u/taha)\ **Replies:** 6\ **Last updated:** [May 26, 2025, 7:34am UTC](https://community.freefem.org/t/coupling-three-equations-for-a-homogenization-problem-with-the-boussinesq-approximation/3936 "2025-05-26T07:34:17Z")
Hello everyone, I’m trying to solve a steady flow with the Boussinesq equation. I have three equations with no nonlinear terms, but I still have this error: ‘End of String could not be found.’ Thank you so much for your … --- ## [Jump condition for elasticity on an interface](https://community.freefem.org/t/jump-condition-for-elasticity-on-an-interface/3930)
**Author:** [@Loic](https://community.freefem.org/u/Loic)\ **Replies:** 10\ **Last updated:** [May 25, 2025, 3:28pm UTC](https://community.freefem.org/t/jump-condition-for-elasticity-on-an-interface/3930 "2025-05-25T15:28:18Z")
Dear all, I would like to add in my variational formulation an expression as the following: \\displaystyle \\frac{\\beta}{h} \\int\_\\Gamma \[u\]\[v\] dS - \\frac{\\beta}{h} \\int\_\\Gamma (\\lambda {\\rm div}(u\_0) I + 2 \\mu \\nabla^… --- ## [How to plot in 3D](https://community.freefem.org/t/how-to-plot-in-3d/3934)
**Author:** [@weixj](https://community.freefem.org/u/weixj)\ **Replies:** 0\ **Last updated:** [May 24, 2025, 1:03pm UTC](https://community.freefem.org/t/how-to-plot-in-3d/3934 "2025-05-24T13:03:46Z")
Now I want to solve the following system Suppose the computational region is \[0,1\]^3 and the mesh Th. For the resulting numerical solutions, I would like to draw the magnetic field lines, velocity streamlines and vec… --- ## [The boundary condition in FreeFem](https://community.freefem.org/t/the-boundary-condition-in-freefem/3932)
**Author:** [@weixj](https://community.freefem.org/u/weixj)\ **Replies:** 1\ **Last updated:** [May 23, 2025, 8:33pm UTC](https://community.freefem.org/t/the-boundary-condition-in-freefem/3932 "2025-05-23T20:33:43Z")
Now, I need to solve the MHD system with the following condition But I don’t know how this boundary condition is represented in the code This is the equations --- ## [P1dc and Dirichlet BC](https://community.freefem.org/t/p1dc-and-dirichlet-bc/3768)
**Author:** [@fb77](https://community.freefem.org/u/fb77)\ **Replies:** 6\ **Last updated:** [May 20, 2025, 10:49am UTC](https://community.freefem.org/t/p1dc-and-dirichlet-bc/3768 "2025-05-20T10:49:08Z")
Hello to everybody, I am wondering why the following simple code fails to set the homogeneous Dirichlet boundary condition to u in P1dc macro dn(u) (N.x\*dx(u)+N.y\*dy(u) ) // def the normal derivative int Nn=8; mesh T… --- ## [What does this error report mean](https://community.freefem.org/t/what-does-this-error-report-mean/3923)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 3\ **Last updated:** [May 20, 2025, 6:02am UTC](https://community.freefem.org/t/what-does-this-error-report-mean/3923 "2025-05-20T06:02:24Z")
Dear all, I am now updating my 2D navier stokes equation with moving boundary to 3D, here is the code Parallel\_3d\_NS\_moving.edp (4.4 KB) Th.mesh (734.3 KB). However, I meet a error report when I run it for some time … --- ## [Default quadrature rule](https://community.freefem.org/t/default-quadrature-rule/415)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 3\ **Last updated:** [May 19, 2025, 8:08am UTC](https://community.freefem.org/t/default-quadrature-rule/415 "2025-05-19T08:08:27Z")
Hello, I have a question about the default choice of quadrature in FreeFEM. Does FreeFEM choose the default quadrature rule to be of highest degree that is exact for the corresponding finite element function? Or do we n… --- ## [Report error when 1 processor but 2 or more is OK](https://community.freefem.org/t/report-error-when-1-processor-but-2-or-more-is-ok/3921)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 2\ **Last updated:** [May 18, 2025, 12:59pm UTC](https://community.freefem.org/t/report-error-when-1-processor-but-2-or-more-is-ok/3921 "2025-05-18T12:59:46Z")
Dear all, Here is my parallel code try\_movemesh.edp (4.0 KB) movemesh.mesh (82.9 KB) I find when I run it with 2 or more processors(ff-mpirun -n 2 try\_movemesh.edp -wg -v 0 ), it can work well. However, when I choo… --- ## [Issue with loading MUMPS plugin in FreeFEM (develop branch) on macOS Apple Silicon after PETSc build](https://community.freefem.org/t/issue-with-loading-mumps-plugin-in-freefem-develop-branch-on-macos-apple-silicon-after-petsc-build/3918)
**Author:** [@ruiruibeauty](https://community.freefem.org/u/ruiruibeauty)\ **Replies:** 3\ **Last updated:** [May 17, 2025, 5:03am UTC](https://community.freefem.org/t/issue-with-loading-mumps-plugin-in-freefem-develop-branch-on-macos-apple-silicon-after-petsc-build/3918 "2025-05-17T05:03:04Z")
Dear FreeFEM Development Team, I am writing to report an issue I’m encountering with loading the MUMPS plugin in FreeFEM on my macOS Apple Silicon system. I have followed the official compilation guide and, per previou… --- ## [Does local mesh keep the region number](https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 2\ **Last updated:** [May 16, 2025, 9:01am UTC](https://community.freefem.org/t/does-local-mesh-keep-the-region-number/3919 "2025-05-16T09:01:47Z")
Dear all, When I parallelize my fsi code, I have a problem about the mesh region number on each local processor. In my sequential code, I separate the conforming mesh as fluid(red color) and solid part(black color) as … --- ## [Strange behavior on the overlapping region](https://community.freefem.org/t/strange-behavior-on-the-overlapping-region/3916)
**Author:** [@quentin](https://community.freefem.org/u/quentin)\ **Replies:** 5\ **Last updated:** [May 15, 2025, 10:41am UTC](https://community.freefem.org/t/strange-behavior-on-the-overlapping-region/3916 "2025-05-15T10:41:04Z")
I am trying to solve a 2D lid-driven cavity in parallel to test numerical schemes. The result sometimes looks strange in the overlapping region. For instance, the code diverges quickly running with -n 4, but shows a plau… --- ## [Mesh3 from MeshS with obstacles](https://community.freefem.org/t/mesh3-from-meshs-with-obstacles/3915)
**Author:** [@Loic](https://community.freefem.org/u/Loic)\ **Replies:** 8\ **Last updated:** [May 14, 2025, 5:07pm UTC](https://community.freefem.org/t/mesh3-from-meshs-with-obstacles/3915 "2025-05-14T17:07:37Z")
Dear all, I have a surface mesh (obstacle.mesh). Next, I create the surface mesh of the bounding box such that the obstacle.mesh is fully including in it. Then when I want to merge the two surface mesh as meshS MESH… --- ## [Problem with peridicity " Periodic: the both number of edges is not the same"](https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914)
**Author:** [@taha](https://community.freefem.org/u/taha)\ **Replies:** 2\ **Last updated:** [May 13, 2025, 3:38pm UTC](https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914 "2025-05-13T15:38:46Z")
diffusion-convection.edp (3.8 KB) Hello everyone,i hove you are doing well,i’m solving a convection-diffution problem in solid/fluid but i’m trying to do a periodicity but it gave me this error " Periodic: the both num… --- ## [Argument Region for int2d function](https://community.freefem.org/t/argument-region-for-int2d-function/3911)
**Author:** [@dominiquebodin](https://community.freefem.org/u/dominiquebodin)\ **Replies:** 1\ **Last updated:** [May 13, 2025, 3:13pm UTC](https://community.freefem.org/t/argument-region-for-int2d-function/3911 "2025-05-13T15:13:23Z")
Dear all, I’m creating a 3D mesh using a geo file from Gmsh. Some labels (integer numbers) defines the boundary surfaces, and it works fine for Dirichlet condition with solve:on(label,condition). For Neumann condition,… --- ## [Can tgv be chosen different values for Mat and vector](https://community.freefem.org/t/can-tgv-be-chosen-different-values-for-mat-and-vector/3913)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 7\ **Last updated:** [May 13, 2025, 8:53am UTC](https://community.freefem.org/t/can-tgv-be-chosen-different-values-for-mat-and-vector/3913 "2025-05-13T08:53:07Z")
Dear all, I find the tgvs are chosen different values for Mat and vector in this code line 34 and 36 laplace-adapt-3d-PETSc.edp (1.9 KB) A = vPoisson(Vh, Vh, tgv = -2); set(A, sparams = “-ksp\_monitor -pc\_type hypre”)… --- ## [Adapt not working properly for a 1D code](https://community.freefem.org/t/adapt-not-working-properly-for-a-1d-code/3906)
**Author:** [@goutham2023](https://community.freefem.org/u/goutham2023)\ **Replies:** 1\ **Last updated:** [May 12, 2025, 7:10am UTC](https://community.freefem.org/t/adapt-not-working-properly-for-a-1d-code/3906 "2025-05-12T07:10:51Z")
Hi FF++ users, I am working on a simple 1D conduction problem that involves material recession. After displacing the mesh using movemesh, I am trying to adapt the mesh using the adaptmesh function. However, it doesn’t s… --- ## [How to trunc in a parallel code](https://community.freefem.org/t/how-to-trunc-in-a-parallel-code/3909)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 7\ **Last updated:** [May 12, 2025, 6:10am UTC](https://community.freefem.org/t/how-to-trunc-in-a-parallel-code/3909 "2025-05-12T06:10:14Z")
Dear all, Is there a command to trunc in parallel code. For example, when I solve fluid structure interaction problem, I need to trunc the solid part. It is easy to implement in sequential code like Ths = trunc(Th,regi… --- ## [Parallel computing error in macOS 15.4](https://community.freefem.org/t/parallel-computing-error-in-macos-15-4/3835)
**Author:** [@Free](https://community.freefem.org/u/Free)\ **Replies:** 9\ **Last updated:** [April 21, 2025, 5:42am UTC](https://community.freefem.org/t/parallel-computing-error-in-macos-15-4/3835 "2025-04-21T05:42:37Z")
Dear all, Since I updated my devices to macOS 15.4, parallel simulations cannot be calculated properly. The following error message appears: user@user 0407 % ff-mpirun -np 2 “/Users/user/Library/Mobile Documents/com~… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=6) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=8)