# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=55 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 56 --- ## [Matrix Inversion and Lapack](https://community.freefem.org/t/matrix-inversion-and-lapack/1262)
**Author:** [@salah](https://community.freefem.org/u/salah)\ **Replies:** 4\ **Last updated:** [October 19, 2021, 8:57am UTC](https://community.freefem.org/t/matrix-inversion-and-lapack/1262 "2021-10-19T08:57:25Z")
Hello FreeFem Community, I’m looking to invert a square matrix A in order to solve the problem Ax=b. The problem is, this matrix A, has no reason to be invertible, so when it’s the case, I would like to compute the more… --- ## [Our company is recruiting a numerical simulation expert (PhD/Post-doctorate level)](https://community.freefem.org/t/our-company-is-recruiting-a-numerical-simulation-expert-phd-post-doctorate-level/1265)
**Author:** [@franck.lahaye](https://community.freefem.org/u/franck.lahaye)\ **Replies:** 0\ **Last updated:** [October 19, 2021, 4:38am UTC](https://community.freefem.org/t/our-company-is-recruiting-a-numerical-simulation-expert-phd-post-doctorate-level/1265 "2021-10-19T04:38:19Z")
Airthium is working on a seasonal energy storage system, our goal is to replace coal and gas fired powerplants by renewables + storage. We are looking for a 3rd numerical simulation specialist to join our team asap. If … --- ## [What the values in output mean?](https://community.freefem.org/t/what-the-values-in-output-mean/1260)
**Author:** [@Jhon](https://community.freefem.org/u/Jhon)\ **Replies:** 2\ **Last updated:** [October 18, 2021, 1:24pm UTC](https://community.freefem.org/t/what-the-values-in-output-mean/1260 "2021-10-18T13:24:17Z")
I write a script to simulate stress and deformation. The “problem” command is used in this script. It is successful to perform the script by command line: “FreeFem++ scriptname.edp” But I can not understand the out… --- ## [Assign a force to boundary node depending on node displacement](https://community.freefem.org/t/assign-a-force-to-boundary-node-depending-on-node-displacement/1254)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 1\ **Last updated:** [October 15, 2021, 1:57am UTC](https://community.freefem.org/t/assign-a-force-to-boundary-node-depending-on-node-displacement/1254 "2021-10-15T01:57:52Z")
So instead of fixing the left edge by saying on(4, u = 0, v =0) I want to assign a force that depends on the displacement. That is a simple string force with a high stiffness coefficient. This was my attempt: // Para… --- ## [Interpolation in parallel](https://community.freefem.org/t/interpolation-in-parallel/1255)
**Author:** [@etj](https://community.freefem.org/u/etj)\ **Replies:** 2\ **Last updated:** [October 14, 2021, 12:47pm UTC](https://community.freefem.org/t/interpolation-in-parallel/1255 "2021-10-14T12:47:34Z")
Hello, I would like to interpolate a FE function computed in parallel with PETSc from a first mesh onto a second mesh. Is that possible? What is the best way to do that? Interpolate() or something else? Is there an exam… --- ## [Building a border from an array of vertices](https://community.freefem.org/t/building-a-border-from-an-array-of-vertices/1253)
**Author:** [@salah](https://community.freefem.org/u/salah)\ **Replies:** 2\ **Last updated:** [October 13, 2021, 8:02am UTC](https://community.freefem.org/t/building-a-border-from-an-array-of-vertices/1253 "2021-10-13T08:02:40Z")
Hello FreeFEM Community, In an attempt to perform some border surgery to get rid of kinks while moving domains I want to rebuild the border of a 2D mesh from a set of vertices (the connectivity of the border - the vert… --- ## [Interface Boundary condition Example](https://community.freefem.org/t/interface-boundary-condition-example/1252)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 0\ **Last updated:** [October 12, 2021, 6:20am UTC](https://community.freefem.org/t/interface-boundary-condition-example/1252 "2021-10-12T06:20:50Z")
Respected @prj and @frederichecht Sir Any example for implementing an interface boundary condition (Neumann) problem would be helpful for my problem. Kindly help me. Thanks --- ## [Reading a txt file: incompatible length error](https://community.freefem.org/t/reading-a-txt-file-incompatible-length-error/1244)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 1\ **Last updated:** [October 5, 2021, 8:48am UTC](https://community.freefem.org/t/reading-a-txt-file-incompatible-length-error/1244 "2021-10-05T08:48:16Z")
Hi, Attached is my txt file (wetransfer link). I want to read the lines from the txt into a variable: string filePath = "../data/"; string fileName = "Heat\_frame\_0.txt"; // Read file. { ifstream file(filePath + f… --- ## [Evolution of mesh and boudaries for FSI problems](https://community.freefem.org/t/evolution-of-mesh-and-boudaries-for-fsi-problems/1248)
**Author:** [@EJariel](https://community.freefem.org/u/EJariel)\ **Replies:** 0\ **Last updated:** [October 5, 2021, 7:43am UTC](https://community.freefem.org/t/evolution-of-mesh-and-boudaries-for-fsi-problems/1248 "2021-10-05T07:43:17Z")
Hello, I need to implement a Fluid-Structure Interaction problem, with a fabric structure immersed in a fluid. The fluid and solid problems would be resolved one after the other at each iteration: at iteration N, we co… --- ## [Label functionality has a bug?](https://community.freefem.org/t/label-functionality-has-a-bug/1243)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 2\ **Last updated:** [October 4, 2021, 5:49pm UTC](https://community.freefem.org/t/label-functionality-has-a-bug/1243 "2021-10-04T17:49:04Z")
Imagine a cube int\[int\] N = \[20, 10, 5\]; // Nodes per side. real \[int, int\] B = \[\[0.0, 1.0\], \[0.0, 0.5\], \[0.0, 0.25\]\]; // Side lengths. int \[int, int\] L = \[\[1, 2\], \[3, 4\], \[5, 6\]\]; // Labels. mesh3 Th = Cube(N, B, L); p… --- ## [Asertion fail for multi-cores](https://community.freefem.org/t/asertion-fail-for-multi-cores/1245)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 1\ **Last updated:** [October 4, 2021, 4:50pm UTC](https://community.freefem.org/t/asertion-fail-for-multi-cores/1245 "2021-10-04T16:50:41Z")
After reading an external mesh file, I got the following assertion fail when using 4 CUPs, but there is no such an error if I use 1 CUP. What’s the problem? --- ## [Phase field fracture Compile error](https://community.freefem.org/t/phase-field-fracture-compile-error/1241)
**Author:** [@nansihu](https://community.freefem.org/u/nansihu)\ **Replies:** 0\ **Last updated:** [October 3, 2021, 8:35am UTC](https://community.freefem.org/t/phase-field-fracture-compile-error/1241 "2021-10-03T08:35:56Z")
I want to finish phase field simulation by Freefem++, but and there is awalys a complile error in the following code: error operator - , \<10LinearCombI7MGauche4C\_F0E\> macro u \[u0,u1\] //eom macro v \[v0,v1\] //eom mac… --- ## [Normal at Surface in 3D cube](https://community.freefem.org/t/normal-at-surface-in-3d-cube/1203)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 0\ **Last updated:** [September 14, 2021, 7:38am UTC](https://community.freefem.org/t/normal-at-surface-in-3d-cube/1203 "2021-09-14T07:38:24Z")
Dear All How can I access the surface boundary of the cube and normal at that Surface? is it ok to express normal as “N = (N.x, N.y, N.Z)” . --- ## [Sorry one vertex of edge is losted](https://community.freefem.org/t/sorry-one-vertex-of-edge-is-losted/1235)
**Author:** [@Pouyan25](https://community.freefem.org/u/Pouyan25)\ **Replies:** 0\ **Last updated:** [September 29, 2021, 8:00am UTC](https://community.freefem.org/t/sorry-one-vertex-of-edge-is-losted/1235 "2021-09-29T08:00:16Z")
hi guys, i am trying to import a mesh in freefem but for producing the finite elements space and setting periodic boundaries i get every time the following error: “sorry one vertex of edge is losted” i tried to reduc… --- ## [MPI across multiple nodes using a container](https://community.freefem.org/t/mpi-across-multiple-nodes-using-a-container/1227)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [September 27, 2021, 10:51am UTC](https://community.freefem.org/t/mpi-across-multiple-nodes-using-a-container/1227 "2021-09-27T10:51:14Z")
Dear all, I found my parallel FreeFem code could not scale across multiple nodes (40 processors per node) on the university’s ARC system, although it scale great on one node (less than 40 processors). Can I ask: Does… --- ## [Error：requiring an unknown u for the problem](https://community.freefem.org/t/error-requiring-an-unknown-u-for-the-problem/1224)
**Author:** [@xiaojiemo](https://community.freefem.org/u/xiaojiemo)\ **Replies:** 4\ **Last updated:** [September 27, 2021, 10:44am UTC](https://community.freefem.org/t/error-requiring-an-unknown-u-for-the-problem/1224 "2021-09-27T10:44:06Z")
I have definite the problem and solve, the software said, I don’t know what is wrong. --- ## [Please help me out! If possible, Could you tell me how to export gradient data?](https://community.freefem.org/t/please-help-me-out-if-possible-could-you-tell-me-how-to-export-gradient-data/1199)
**Author:** [@sosome](https://community.freefem.org/u/sosome)\ **Replies:** 2\ **Last updated:** [September 27, 2021, 10:43am UTC](https://community.freefem.org/t/please-help-me-out-if-possible-could-you-tell-me-how-to-export-gradient-data/1199 "2021-09-27T10:43:47Z")
Dear all, I am trying to export gradient data from the required 2D poison’ equation, but I am not sure how to export the solution and gradient from the 2d poisson equation in document code. I believe exporting dx(), dy… --- ## [I have three Questions about the Poisson eqation and solution!](https://community.freefem.org/t/i-have-three-questions-about-the-poisson-eqation-and-solution/1226)
**Author:** [@sosome](https://community.freefem.org/u/sosome)\ **Replies:** 0\ **Last updated:** [September 27, 2021, 9:59am UTC](https://community.freefem.org/t/i-have-three-questions-about-the-poisson-eqation-and-solution/1226 "2021-09-27T09:59:50Z")
In the Poisson equation, when Dirichlet Boundary condition is u=0, I want to solve the problem through the general polygon mesh. poisson equation Please see these three questions. For the situation above, does re… --- ## [Try to get unset x,y](https://community.freefem.org/t/try-to-get-unset-x-y/1225)
**Author:** [@xiaojiemo](https://community.freefem.org/u/xiaojiemo)\ **Replies:** 0\ **Last updated:** [September 27, 2021, 2:51am UTC](https://community.freefem.org/t/try-to-get-unset-x-y/1225 "2021-09-27T02:51:31Z")
here is the code and the software told me there was an error.Please help me out!! border lower(t=0,410){x=t;y=0;} border right(t=0,91){x=410;y=t;} border upper(t=410,0){x=t;y=91;} border left(t=91,0){x=0;y=t;} int c… --- ## [Try to get unset x,y,](https://community.freefem.org/t/try-to-get-unset-x-y/584)
**Author:** [@candy](https://community.freefem.org/u/candy)\ **Replies:** 5\ **Last updated:** [September 26, 2021, 7:14am UTC](https://community.freefem.org/t/try-to-get-unset-x-y/584 "2021-09-26T07:14:52Z")
Hello， I am solving a large sysytem, my idea is to decouple it. But my code can be run in 2D, it gives errors in 3D. It says Try to get unset x,y, … Did you see some similar error? Could you give me some insights? --- ## [How can i make a T-shaped mesh](https://community.freefem.org/t/how-can-i-make-a-t-shaped-mesh/1215)
**Author:** [@DanielaV](https://community.freefem.org/u/DanielaV)\ **Replies:** 5\ **Last updated:** [September 23, 2021, 11:31pm UTC](https://community.freefem.org/t/how-can-i-make-a-t-shaped-mesh/1215 "2021-09-23T23:31:14Z")
Hello there, how can i make a T-shaped mesh I have tried and it does not come out --- ## [Inflow and outflow direction](https://community.freefem.org/t/inflow-and-outflow-direction/1222)
**Author:** [@erdo](https://community.freefem.org/u/erdo)\ **Replies:** 0\ **Last updated:** [September 22, 2021, 6:16pm UTC](https://community.freefem.org/t/inflow-and-outflow-direction/1222 "2021-09-22T18:16:09Z")
Hello, I work navier stokes flow on a rectengular domain. And i want to control inflow and outflow direction of fluid as the picture below. How can i do this? Thank you int nn = 10; //number of nodes by un… --- ## [Lost labels after Tetgen](https://community.freefem.org/t/lost-labels-after-tetgen/1219)
**Author:** [@tess35](https://community.freefem.org/u/tess35)\ **Replies:** 0\ **Last updated:** [September 22, 2021, 4:03pm UTC](https://community.freefem.org/t/lost-labels-after-tetgen/1219 "2021-09-22T16:03:03Z")
Hi All, I have the same problem that " Assigning labels to surface mesh - #3 by Alex ", but my errors remain. All the labels after meshing with Tetgen are lost. Here a extract , to create a rectangular parallelepiped … --- ## [OS Differences: Windows vs. Mac/Linux v4.9](https://community.freefem.org/t/os-differences-windows-vs-mac-linux-v4-9/1218)
**Author:** [@willrey](https://community.freefem.org/u/willrey)\ **Replies:** 0\ **Last updated:** [September 22, 2021, 2:15pm UTC](https://community.freefem.org/t/os-differences-windows-vs-mac-linux-v4-9/1218 "2021-09-22T14:15:48Z")
FreeFem++ v4.9 We’re seeing different solutions and meshing between Windows (Dell XPS) and Mac/Linux (Macbook Pro M1). It is frequently so extreme that when solving the Laplace equation for our electromagnetics problem,… --- ## [Save figure with plotMPI](https://community.freefem.org/t/save-figure-with-plotmpi/1217)
**Author:** [@yhao](https://community.freefem.org/u/yhao)\ **Replies:** 2\ **Last updated:** [September 22, 2021, 10:17am UTC](https://community.freefem.org/t/save-figure-with-plotmpi/1217 "2021-09-22T10:17:33Z")
Dear all, I am now working on the neo-Hookean model in parallelization. Is there any way to save the figure plot by plotMPI? Thanks in advance. --- ## [Mesh Adaption at an arbitrary list of boundaries](https://community.freefem.org/t/mesh-adaption-at-an-arbitrary-list-of-boundaries/1216)
**Author:** [@kevinmo08](https://community.freefem.org/u/kevinmo08)\ **Replies:** 0\ **Last updated:** [September 21, 2021, 7:33pm UTC](https://community.freefem.org/t/mesh-adaption-at-an-arbitrary-list-of-boundaries/1216 "2021-09-21T19:33:43Z")
Hi all, I am trying to calculate a convection diffusion equation in 3 dimensions, but I know that my problem will have a boundary layer near a 2D wall. I create a 2D mesh first, and then extended it into 3D. What I wan… --- ## [Solve U=K^-1.F using stiffness matrix for vector fields](https://community.freefem.org/t/solve-u-k-1-f-using-stiffness-matrix-for-vector-fields/604)
**Author:** [@pdapte1999](https://community.freefem.org/u/pdapte1999)\ **Replies:** 12\ **Last updated:** [September 19, 2021, 7:49pm UTC](https://community.freefem.org/t/solve-u-k-1-f-using-stiffness-matrix-for-vector-fields/604 "2021-09-19T19:49:53Z")
Dear all, I am trying to solve problem of 3-dimensional elasticity. I have extracted the stiffness matrix (K) and force vector (F) using the variational formulation. Now, I have solved the equation for displacement U, u… --- ## [Large scale FSI implementation](https://community.freefem.org/t/large-scale-fsi-implementation/1214)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 2\ **Last updated:** [September 17, 2021, 3:06pm UTC](https://community.freefem.org/t/large-scale-fsi-implementation/1214 "2021-09-17T15:06:17Z")
Is a parallel implementation of 3d fluid-struction interaction algorithm (no matter what types of algorithm) in freefem, a paper or a piece of code? --- ## [Compile error in a problem definition](https://community.freefem.org/t/compile-error-in-a-problem-definition/1212)
**Author:** [@xiaojiemo](https://community.freefem.org/u/xiaojiemo)\ **Replies:** 4\ **Last updated:** [September 16, 2021, 12:43pm UTC](https://community.freefem.org/t/compile-error-in-a-problem-definition/1212 "2021-09-16T12:43:05Z")
hello, I meet some trouble in problem definition. problem order(fi,dfi)=int2d(th1)(dfialphafi/M) -int2d(th1)(dfidpfi(rawf\*(cl-ci)(setaf1log(setaf1/273.15)-setaf1+seff)) +int2d(th1)(dfidpfirawf\*(sl-si)seff(setaf1-seff)… --- ## [About syntax error](https://community.freefem.org/t/about-syntax-error/1182)
**Author:** [@xiaojiemo](https://community.freefem.org/u/xiaojiemo)\ **Replies:** 3\ **Last updated:** [September 16, 2021, 6:10am UTC](https://community.freefem.org/t/about-syntax-error/1182 "2021-09-16T06:10:06Z")
I’m trying to write a problem about the equation like below, and I wrote: problem displacementf(uf,duf)=int2d(th2)((dx(duf)\*dx(uf)+dy(duf)\*dy(uf))\*uf)-int2d(th2)((dx(duf)\*dx(uf)+dy(duf)\*dy(uf))\*convect(\[up1,up2\],-dt,… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=54) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=56)