# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=56 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 57 --- ## [Operation error in problem definition](https://community.freefem.org/t/operation-error-in-problem-definition/466)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 20\ **Last updated:** [September 15, 2021, 2:16pm UTC](https://community.freefem.org/t/operation-error-in-problem-definition/466 "2021-09-15T14:16:52Z")
Dear all, I have defined a problem based on a non-dimensionalized coupled equation. Unfortunately, I am getting an OPERATIONAL error in spite of having a correct operation( as per my weak formulation). I have writte… --- ## [Writing data on a clustered file system](https://community.freefem.org/t/writing-data-on-a-clustered-file-system/1201)
**Author:** [@Markov](https://community.freefem.org/u/Markov)\ **Replies:** 10\ **Last updated:** [September 15, 2021, 9:51am UTC](https://community.freefem.org/t/writing-data-on-a-clustered-file-system/1201 "2021-09-15T09:51:39Z")
Hello, I have a code that runs on parallel and at the end it writes the solution on a file. When I run it on my Mac everything is ok however, when running it on a cluster I get each time a different result, I don’t get … --- ## [Modifier la police pour un text string sous la commande "cmm"](https://community.freefem.org/t/modifier-la-police-pour-un-text-string-sous-la-commande-cmm/1205)
**Author:** [@Kamal\_FEM](https://community.freefem.org/u/Kamal_FEM)\ **Replies:** 2\ **Last updated:** [September 15, 2021, 9:35am UTC](https://community.freefem.org/t/modifier-la-police-pour-un-text-string-sous-la-commande-cmm/1205 "2021-09-15T09:35:07Z")
Bonjour, j’aimerais bien modifier le texte dans l’affichage dans mon “plot”. Mon objectif c’est d’afficher plusieurs valeurs au même temps sous la commande “cmm” du coup ça ne s’affiche pas entierement car c’est très lo… --- ## [From generic element to periodic element](https://community.freefem.org/t/from-generic-element-to-periodic-element/1188)
**Author:** [@Neutrino](https://community.freefem.org/u/Neutrino)\ **Replies:** 2\ **Last updated:** [September 15, 2021, 8:31am UTC](https://community.freefem.org/t/from-generic-element-to-periodic-element/1188 "2021-09-15T08:31:44Z")
Hi there! So I have the following problem. I have two finite element spaces over a square domain in my program: fespace Vh(Th, P1); fespace Vhp( Th , P1 , periodic = \[ \[2,y\],\[4,y\],\[1,x\],\[3,x\] \]); I have an element … --- ## [Finite volume method](https://community.freefem.org/t/finite-volume-method/1206)
**Author:** [@Jamal](https://community.freefem.org/u/Jamal)\ **Replies:** 0\ **Last updated:** [September 14, 2021, 3:18pm UTC](https://community.freefem.org/t/finite-volume-method/1206 "2021-09-14T15:18:22Z")
Hello everyone; How to solve the Poisson’s equation using FVM in freefem --- ## [The problem of solving pressure(p) in 3D](https://community.freefem.org/t/the-problem-of-solving-pressure-p-in-3d/65)
**Author:** [@xlzheng](https://community.freefem.org/u/xlzheng)\ **Replies:** 2\ **Last updated:** [September 14, 2021, 7:13am UTC](https://community.freefem.org/t/the-problem-of-solving-pressure-p-in-3d/65 "2021-09-14T07:13:52Z")
Hi, I want to solve pressure with the initial velocity in 3d, but it doesn’t work, the variational equation comes from the following N-S equation: the program as follows: // load "msh3" load "tetgen" load "medit" … --- ## [Problem with variational formulation](https://community.freefem.org/t/problem-with-variational-formulation/1193)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 1\ **Last updated:** [September 13, 2021, 11:23am UTC](https://community.freefem.org/t/problem-with-variational-formulation/1193 "2021-09-13T11:23:16Z")
Hi, i have to program the following system du1/dt =D1d^2u1/dx^2 +a1u1\*(1-u1-u2) du2/dt=D2d^2u2/dx^2 +a2(u2+epsu1)\*(1-u1-u2) in the space and time intervals: 0\ **Author:** [@NearAmvil](https://community.freefem.org/u/NearAmvil)\ **Replies:** 4\ **Last updated:** [September 9, 2021, 3:08pm UTC](https://community.freefem.org/t/missing-the-first-eigenvector-eigenvalue/1167 "2021-09-09T15:08:00Z") Hello ! I’m currectly using FreeFEM++ to compute electronic structures. I wrote a FreeFREM++ code supposed to compute the lowest eigenvalues and eigenfunctions of the Schrödinger equation in 2D, that is to solve the el… --- ## [News from the StabFem project](https://community.freefem.org/t/news-from-the-stabfem-project/1195)
**Author:** [@david.fabre](https://community.freefem.org/u/david.fabre)\ **Replies:** 0\ **Last updated:** [September 8, 2021, 8:57am UTC](https://community.freefem.org/t/news-from-the-stabfem-project/1195 "2021-09-08T08:57:15Z")
Dear FF developers and users, We are happy to announce a new release 3.9 of the StabFem project. StabFem is a Matlab/Octave interface to FreeFem which allows to launch your programs, manipulate and plot your results, s… --- ## [PETSc operators](https://community.freefem.org/t/petsc-operators/1191)
**Author:** [@Markov](https://community.freefem.org/u/Markov)\ **Replies:** 9\ **Last updated:** [September 6, 2021, 7:16pm UTC](https://community.freefem.org/t/petsc-operators/1191 "2021-09-06T19:16:57Z")
How to perform simple operations in PETSc like matrix addition, multiplication, constant times a matrix? I’ve tried MatMatMult and MatScale both did not work. --- ## [Transient elasticity problem: sequential vs parallel](https://community.freefem.org/t/transient-elasticity-problem-sequential-vs-parallel/1186)
**Author:** [@Markov](https://community.freefem.org/u/Markov)\ **Replies:** 15\ **Last updated:** [September 3, 2021, 12:50pm UTC](https://community.freefem.org/t/transient-elasticity-problem-sequential-vs-parallel/1186 "2021-09-03T12:50:33Z")
Hello, I am trying to solve the transient elasticity equation using the New-Mark Beta algorithm. The code is able to yield correct results when I run it on a single proc, however when switching to parallel the results b… --- ## [K-d tree support in FreeFEM](https://community.freefem.org/t/k-d-tree-support-in-freefem/1187)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 0\ **Last updated:** [September 2, 2021, 7:17am UTC](https://community.freefem.org/t/k-d-tree-support-in-freefem/1187 "2021-09-02T07:17:57Z")
Hi, Is there any k-d tree support in freefem? Perhaps with examples? Thank you --- ## [Conversion from array to finite element space variable](https://community.freefem.org/t/conversion-from-array-to-finite-element-space-variable/1185)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 2\ **Last updated:** [September 1, 2021, 10:08am UTC](https://community.freefem.org/t/conversion-from-array-to-finite-element-space-variable/1185 "2021-09-01T10:08:09Z")
Hi, Variable initialization: fespace Nh(Th, \[P1, P1\]); // FEM variables. Nh \[u1, u2\], \[v1, v2\]; So elasticity problem can be solved like this problem elas(\[u1,u2\],\[v1,v2\]) = int2d(Th)( lam\*div(u1,u2)\*div(v1,… --- ## [3D geometry 'interrupted' between inlet and outlet](https://community.freefem.org/t/3d-geometry-interrupted-between-inlet-and-outlet/1128)
**Author:** [@chr222](https://community.freefem.org/u/chr222)\ **Replies:** 4\ **Last updated:** [September 1, 2021, 8:30am UTC](https://community.freefem.org/t/3d-geometry-interrupted-between-inlet-and-outlet/1128 "2021-09-01T08:30:59Z")
Dear all, I am running into a problem while adapting a 2D U-channel flow into 3D. I am using this NS solver and the buildlayers command to ‘extrude’ the previously used 2D geometry. When checking the results it seems as… --- ## [About why the Dirac-delta is not belong to H^-1 or H^1?](https://community.freefem.org/t/about-why-the-dirac-delta-is-not-belong-to-h-1-or-h-1/1181)
**Author:** [@HGH](https://community.freefem.org/u/HGH)\ **Replies:** 0\ **Last updated:** [August 29, 2021, 6:14am UTC](https://community.freefem.org/t/about-why-the-dirac-delta-is-not-belong-to-h-1-or-h-1/1181 "2021-08-29T06:14:13Z")
Hi FreeFEM++ developers and users I have a question, About why the Dirac-delta is not belong to H^-1 or H^1? Who can explain it? --- ## [About tetgen using](https://community.freefem.org/t/about-tetgen-using/1180)
**Author:** [@Pablo](https://community.freefem.org/u/Pablo)\ **Replies:** 1\ **Last updated:** [August 28, 2021, 2:59pm UTC](https://community.freefem.org/t/about-tetgen-using/1180 "2021-08-28T14:59:33Z")
My question is about the example “cube with balloon” ( from manual ). How can I use Tetgen to do a cube without a balloon?. This is the problem, the streamlines don’t see an internal surface (for example balloon) as an… --- ## [Material derivative](https://community.freefem.org/t/material-derivative/1179)
**Author:** [@xiaojiemo](https://community.freefem.org/u/xiaojiemo)\ **Replies:** 0\ **Last updated:** [August 27, 2021, 7:40am UTC](https://community.freefem.org/t/material-derivative/1179 "2021-08-27T07:40:34Z")
Dear FreeFEM users, I would like to ask a question about material derivative, whose form is D(X)=dx/dt+vx\*gradx. how to define it ? --- ## [Two-dimensional elasticity problem using variational definition](https://community.freefem.org/t/two-dimensional-elasticity-problem-using-variational-definition/1177)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 4\ **Last updated:** [August 27, 2021, 6:11am UTC](https://community.freefem.org/t/two-dimensional-elasticity-problem-using-variational-definition/1177 "2021-08-27T06:11:35Z")
Mission Consider a plane (a\*b rectangular). On the left side, the edge is attached to a wall but can move freely along a vertical axis. On the right side, a pressure p is applied that stretches the plate. A sketch: A… --- ## [All the nodes connected to a specified one](https://community.freefem.org/t/all-the-nodes-connected-to-a-specified-one/1178)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [August 25, 2021, 10:29am UTC](https://community.freefem.org/t/all-the-nodes-connected-to-a-specified-one/1178 "2021-08-25T10:29:19Z")
Given a node of a mesh, what’s the quick method to find all the nodes connected to it? It is not straightforward to print this information using Th.nv, Th.nt, Th.nbe --- ## [Barycenter refined meshes](https://community.freefem.org/t/barycenter-refined-meshes/1176)
**Author:** [@candy](https://community.freefem.org/u/candy)\ **Replies:** 2\ **Last updated:** [August 25, 2021, 7:12am UTC](https://community.freefem.org/t/barycenter-refined-meshes/1176 "2021-08-25T07:12:13Z")
Hello, I need the barycenter refined meshes by using FreeFEM. Does anyone have any idea about that? Thanks in advance. Best regards, Canddy --- ## [Splitmesh in 3D](https://community.freefem.org/t/splitmesh-in-3d/1170)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 1\ **Last updated:** [August 24, 2021, 2:35pm UTC](https://community.freefem.org/t/splitmesh-in-3d/1170 "2021-08-24T14:35:57Z")
In 3D, is there a similar command as 2D splitmesh() or trunc() which can locally split a mesh as shown in following figures? More generally, can we locally refine a mesh in FreeFem (without changing the elements far away… --- ## [Change the label of a region / some elements](https://community.freefem.org/t/change-the-label-of-a-region-some-elements/1171)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [August 24, 2021, 2:28pm UTC](https://community.freefem.org/t/change-the-label-of-a-region-some-elements/1171 "2021-08-24T14:28:21Z")
Dear all, If we have a large mesh Th and a small mesh Ths on top of it, we know interpolate() or transferMat() can provide the interpolation matrix between these two meshes. My questions are: can we print the elemen… --- ## [Apply pressure to edge for elasticity problem](https://community.freefem.org/t/apply-pressure-to-edge-for-elasticity-problem/1169)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 0\ **Last updated:** [August 23, 2021, 9:53am UTC](https://community.freefem.org/t/apply-pressure-to-edge-for-elasticity-problem/1169 "2021-08-23T09:53:40Z")
Problem So I have a simple rectangular domain with x = 1 m and y = 0.5 m. What I want to compute is a steady state if pressure P is applied to the left and right vertical side. Attempt at solution load "medit" // Gener… --- ## [An error while trying to use periodic boundaries](https://community.freefem.org/t/an-error-while-trying-to-use-periodic-boundaries/1168)
**Author:** [@Pouyan25](https://community.freefem.org/u/Pouyan25)\ **Replies:** 0\ **Last updated:** [August 23, 2021, 8:16am UTC](https://community.freefem.org/t/an-error-while-trying-to-use-periodic-boundaries/1168 "2021-08-23T08:16:45Z")
Hi guys, i have atoruble while trying to use perodic boundries. I am trying to solve the diffusion equation for a rectangle shpae in 2D and now when i try to use the boundry condition I recieve an error which says: Ass… --- ## [Imorting 2D geometry from Salome in FreeFem++](https://community.freefem.org/t/imorting-2d-geometry-from-salome-in-freefem/1132)
**Author:** [@Pouyan25](https://community.freefem.org/u/Pouyan25)\ **Replies:** 2\ **Last updated:** [August 23, 2021, 8:10am UTC](https://community.freefem.org/t/imorting-2d-geometry-from-salome-in-freefem/1132 "2021-08-23T08:10:30Z")
Hi there, i am very confused about a one problem with FreeFem. I am trying to import a 2D Geometry from Salome in FreeFem. So first i sketched the geometry in Salome and then i saved it with “.brep” format. After that i… --- ## [Unexpected array behaviour](https://community.freefem.org/t/unexpected-array-behaviour/1166)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 0\ **Last updated:** [August 20, 2021, 8:45am UTC](https://community.freefem.org/t/unexpected-array-behaviour/1166 "2021-08-20T08:45:49Z")
My mesh is defined as follows int\[int\] Nxyz=\[20,5,5\]; real \[int,int\] Bxyz=\[\[0.,5.\],\[0.,1.\],\[0.,1.\]\]; int \[int,int\] Lxyz=\[\[1,2\],\[2,2\],\[2,2\]\]; mesh3 Th=Cube(Nxyz,Bxyz,Lxyz); and my fespace fespace Vh(Th,\[P1,P1,P1\]); … --- ## [Type mismatch when using varf](https://community.freefem.org/t/type-mismatch-when-using-varf/1165)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 0\ **Last updated:** [August 20, 2021, 6:59am UTC](https://community.freefem.org/t/type-mismatch-when-using-varf/1165 "2021-08-20T06:59:11Z")
Problem So I took this example and my goal is to rewrite it using varf functionality and get the same results. Note The usage of varf is explained here on a 2D and 3D Poisson problem. load "msh3" //import three-dimensi… --- ## [Problem during factorization of a system of reaction diffusion equations](https://community.freefem.org/t/problem-during-factorization-of-a-system-of-reaction-diffusion-equations/1162)
**Author:** [@Jacoban90](https://community.freefem.org/u/Jacoban90)\ **Replies:** 1\ **Last updated:** [August 19, 2021, 12:51pm UTC](https://community.freefem.org/t/problem-during-factorization-of-a-system-of-reaction-diffusion-equations/1162 "2021-08-19T12:51:21Z")
Hello, I was trying to represent the weak formula of the following system of reaction diffusion equations Where the main variables Cm and Ce are the ester and monomer concentrations as you can see in the fórmula. The… --- ## [Log file creation](https://community.freefem.org/t/log-file-creation/1160)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 1\ **Last updated:** [August 17, 2021, 8:58am UTC](https://community.freefem.org/t/log-file-creation/1160 "2021-08-17T08:58:27Z")
Hello, Is it possible that we create a log file from .edp files output simulations? I need to save all the data that is being printed in terminal in a log (txt) file. Thanks. --- ## [Problem with medit in Freefem++ vesrsion 4.9](https://community.freefem.org/t/problem-with-medit-in-freefem-vesrsion-4-9/1159)
**Author:** [@ali.mes](https://community.freefem.org/u/ali.mes)\ **Replies:** 2\ **Last updated:** [August 16, 2021, 1:12pm UTC](https://community.freefem.org/t/problem-with-medit-in-freefem-vesrsion-4-9/1159 "2021-08-16T13:12:32Z")
When I run the following code load “medit” mesh Th=square(10,10,\[2x-1,2y-1\]); fespace Vh(Th,P1); Vh u=2-xx-yy; medit(“mm”,Th,u); I get a back and white flat triangulated square, but the manual mentioned that this c… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=55) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=57)