# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=24 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 25 --- ## [Exponential runge kutta?](https://community.freefem.org/t/exponential-runge-kutta/2894)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 0\ **Last updated:** [January 19, 2024, 4:14pm UTC](https://community.freefem.org/t/exponential-runge-kutta/2894 "2024-01-19T16:14:30Z")
I think in the past I made some comment about exponentials seeming like natural solution families for a lot of equations even without fourier, laplace. On some literature searching, I found something called exponentia… --- ## [The answer doesn't converge by refining the mesh](https://community.freefem.org/t/the-answer-doesnt-converge-by-refining-the-mesh/2883)
**Author:** [@m.javad98](https://community.freefem.org/u/m.javad98)\ **Replies:** 5\ **Last updated:** [January 17, 2024, 6:35pm UTC](https://community.freefem.org/t/the-answer-doesnt-converge-by-refining-the-mesh/2883 "2024-01-17T18:35:48Z")
Hi, I am trying to solve a BVP to obtain the micropolar strain localization tensor in a 2D chiral geometry with some periodic boundary conditions. I have 2 unknowns h111 and h211. The boundary conditions are: h111(-0.5… --- ## [Complex matrix for EPSSolve](https://community.freefem.org/t/complex-matrix-for-epssolve/2886)
**Author:** [@PaulGomezz](https://community.freefem.org/u/PaulGomezz)\ **Replies:** 4\ **Last updated:** [January 17, 2024, 7:50am UTC](https://community.freefem.org/t/complex-matrix-for-epssolve/2886 "2024-01-17T07:50:30Z")
Hi, I’m trying to convert a complex matrix AA into a matrix named dA via this method : matrix\ AA = a(Vh,Vh,solver = sparsesolver); matrix\ BB = b(Vh,Vh,solver = sparsesolver); Mat\ … --- ## [Periodic Boundary Conditions for a 2D Problem](https://community.freefem.org/t/periodic-boundary-conditions-for-a-2d-problem/2859)
**Author:** [@m.javad98](https://community.freefem.org/u/m.javad98)\ **Replies:** 2\ **Last updated:** [January 15, 2024, 1:50pm UTC](https://community.freefem.org/t/periodic-boundary-conditions-for-a-2d-problem/2859 "2024-01-15T13:50:02Z")
Hi, I am new to FreeFem++, and I am trying to solve a BVP to obtain the micropolar strain localization tensor in a 2D square with some periodic boundary conditions that its dimensions are as follows: \[-0.5,0.5\]×\[-0.5,0.5… --- ## [How to implement an operator at the boundary?](https://community.freefem.org/t/how-to-implement-an-operator-at-the-boundary/2862)
**Author:** [@C98](https://community.freefem.org/u/C98)\ **Replies:** 6\ **Last updated:** [January 14, 2024, 3:44pm UTC](https://community.freefem.org/t/how-to-implement-an-operator-at-the-boundary/2862 "2024-01-14T15:44:51Z")
Hi, I am considering the heat equation u\_t = \\Delta u on a plate \[0,1\]\\times \[0,1\]. I would like to impose, in FreeFem, the following type of boundary condition u(x,0) = F\\bigg(\\int\_{0}^{1}u(x,y)dy \\bigg) for x\\in (… --- ## [Moving interface and remesh across cores in parallel](https://community.freefem.org/t/moving-interface-and-remesh-across-cores-in-parallel/1023)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 4\ **Last updated:** [January 14, 2024, 3:38am UTC](https://community.freefem.org/t/moving-interface-and-remesh-across-cores-in-parallel/1023 "2024-01-14T03:38:42Z")
Dear all, I am dealing with a moving interface FSI problem, and need to remesh after several steps of moving the old mesh… For a serial code, I just track the fluid-solid interface using extractborder(), and after seve… --- ## [Piezoelectric vibration simulation in FreeFEM](https://community.freefem.org/t/piezoelectric-vibration-simulation-in-freefem/2880)
**Author:** [@solerzhuxy](https://community.freefem.org/u/solerzhuxy)\ **Replies:** 0\ **Last updated:** [January 14, 2024, 2:22am UTC](https://community.freefem.org/t/piezoelectric-vibration-simulation-in-freefem/2880 "2024-01-14T02:22:48Z")
Hi, I am interested in simulate piezoelectric vibration by FreeFEM. I see an example on the website. I am curious about the capability of 3D vibration model with preload on the piezoelectric material. If multiple materia… --- ## [Domain and Pressure](https://community.freefem.org/t/domain-and-pressure/2879)
**Author:** [@Efe\_Taner](https://community.freefem.org/u/Efe_Taner)\ **Replies:** 2\ **Last updated:** [January 13, 2024, 1:45pm UTC](https://community.freefem.org/t/domain-and-pressure/2879 "2024-01-13T13:45:21Z")
Hello, I try to solve the base flow of a hated cylinder (2D)(natural convection) and try to understand the outer domain and pressure relationship. However, the pressure values sometimes increase and decrease when the do… --- ## [The meaning of "clean = true" in the "Mat\ M(J, Loc, clean = true);"](https://community.freefem.org/t/the-meaning-of-clean-true-in-the-mat-complex-m-j-loc-clean-true/2877)
**Author:** [@WeiQLiu](https://community.freefem.org/u/WeiQLiu)\ **Replies:** 2\ **Last updated:** [January 12, 2024, 7:18am UTC](https://community.freefem.org/t/the-meaning-of-clean-true-in-the-mat-complex-m-j-loc-clean-true/2877 "2024-01-12T07:18:17Z")
Dear all, I have recently been studying Eigenvalue problem in PETSc. This is FreeFem-sources/examples/hpddm–Eigenvalue problems. I find that some script have parameter “clean = true” in “Mat M(J, Loc, clean = true)”, … --- ## [Lift and drag over a cylinder](https://community.freefem.org/t/lift-and-drag-over-a-cylinder/2654)
**Author:** [@Erika](https://community.freefem.org/u/Erika)\ **Replies:** 4\ **Last updated:** [January 11, 2024, 8:09am UTC](https://community.freefem.org/t/lift-and-drag-over-a-cylinder/2654 "2024-01-11T08:09:57Z")
Hello everyone, I am writing a mesh code and I need to compute the lift and the drag over a cylindrical surface. The computation I need to implement is the following one: and I have tried to implement them in the foll… --- ## [Anyone tried using the Paraview in-situ interface with FF?](https://community.freefem.org/t/anyone-tried-using-the-paraview-in-situ-interface-with-ff/2876)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 0\ **Last updated:** [January 10, 2024, 5:59pm UTC](https://community.freefem.org/t/anyone-tried-using-the-paraview-in-situ-interface-with-ff/2876 "2024-01-10T17:59:52Z")
Has anyone looked at interfacing FF to PAraview using their “in-situ” interface? I had a few responses here, paraview discussion as I was looking for things similar to mjmdatascope I’ve never used Paraview to any gr… --- ## [Arpack Error Max\_Iteration](https://community.freefem.org/t/arpack-error-max-iteration/2875)
**Author:** [@Efe\_Taner](https://community.freefem.org/u/Efe_Taner)\ **Replies:** 0\ **Last updated:** [January 10, 2024, 4:35pm UTC](https://community.freefem.org/t/arpack-error-max-iteration/2875 "2024-01-10T16:35:43Z")
Hello To calculate linear stability (eigenmodes), I have faced arpack error max iteration. matrix A=matrixA(Mh,Mh, solver=UMFPACK); matrix b=matrixB(Mh,Mh, solver=UMFPACK); int k=EigenValue(A,b, sigma = sig , nev=nev… --- ## [Cartesian to polar using movemesh](https://community.freefem.org/t/cartesian-to-polar-using-movemesh/2874)
**Author:** [@RaghunathBandha](https://community.freefem.org/u/RaghunathBandha)\ **Replies:** 1\ **Last updated:** [January 10, 2024, 2:12pm UTC](https://community.freefem.org/t/cartesian-to-polar-using-movemesh/2874 "2024-01-10T14:12:01Z")
movemesh.edp (148 Bytes) I am trying to transfer cartesian coordinate to polar by using movemesh, I am getting error due to inverse tan function for (0,0). How to resolve the issue? Please help. Shall I need to define … --- ## [Combine Multiple Meshes](https://community.freefem.org/t/combine-multiple-meshes/2872)
**Author:** [@YOuungLi](https://community.freefem.org/u/YOuungLi)\ **Replies:** 0\ **Last updated:** [January 9, 2024, 3:29pm UTC](https://community.freefem.org/t/combine-multiple-meshes/2872 "2024-01-09T15:29:30Z")
Dear All, I’m encountering an error while attempting to combine multiple meshes, and I’m having trouble understanding why this error persists even after adjusting the orientation. error : “Bug in mortar constrution : c… --- ## [PETSc - createMat Issues](https://community.freefem.org/t/petsc-createmat-issues/2868)
**Author:** [@OTTAVIO.C.T.UNISA](https://community.freefem.org/u/OTTAVIO.C.T.UNISA)\ **Replies:** 4\ **Last updated:** [January 9, 2024, 11:43am UTC](https://community.freefem.org/t/petsc-createmat-issues/2868 "2024-01-09T11:43:12Z")
Good morning everyone. I have been practising with FreeFem++ (Windows 11) for a couple of months and now i’m catching up with expert tutorial 2022 made by Professor Pierre Joliviet in order to learn parallel computing. I… --- ## [Facemerge is not a parameter of movemesh?](https://community.freefem.org/t/facemerge-is-not-a-parameter-of-movemesh/1608)
**Author:** [@wby](https://community.freefem.org/u/wby)\ **Replies:** 1\ **Last updated:** [January 7, 2024, 1:45am UTC](https://community.freefem.org/t/facemerge-is-not-a-parameter-of-movemesh/1608 "2024-01-07T01:45:31Z")
I try to use facemerge=1, but it can’t recognize. --- ## [Choosing save path for vtk files](https://community.freefem.org/t/choosing-save-path-for-vtk-files/2867)
**Author:** [@OTTAVIO.C.T.UNISA](https://community.freefem.org/u/OTTAVIO.C.T.UNISA)\ **Replies:** 4\ **Last updated:** [January 6, 2024, 6:37pm UTC](https://community.freefem.org/t/choosing-save-path-for-vtk-files/2867 "2024-01-06T18:37:51Z")
Good morning everyone. I have been practising with FreeFem++ (Windows 11) for a couple of months and now i’m catching up with expert tutorial 2022 made by Professor Pierre Joliviet in order to learn parallel computing. I… --- ## [ICCG with accleration in PETSc](https://community.freefem.org/t/iccg-with-accleration-in-petsc/2865)
**Author:** [@ksugahar](https://community.freefem.org/u/ksugahar)\ **Replies:** 1\ **Last updated:** [January 6, 2024, 6:26am UTC](https://community.freefem.org/t/iccg-with-accleration-in-petsc/2865 "2024-01-06T06:26:59Z")
I am trying to solve my problem by ICCG with an acceleration factor. The method itself is described in the following article. I am trying to find a way to do the acceleraion with PETSc, but so far I have not found a w… --- ## [How to use union of two different meshes in a single integration? Where I am doing the mistake?](https://community.freefem.org/t/how-to-use-union-of-two-different-meshes-in-a-single-integration-where-i-am-doing-the-mistake/2841)
**Author:** [@RaghunathBandha](https://community.freefem.org/u/RaghunathBandha)\ **Replies:** 16\ **Last updated:** [January 5, 2024, 1:09am UTC](https://community.freefem.org/t/how-to-use-union-of-two-different-meshes-in-a-single-integration-where-i-am-doing-the-mistake/2841 "2024-01-05T01:09:37Z")
int n=32; int m=ceil(2n/pi); border C1(t=0,pi){x=cos(t); y=sin(t);label=1;} border C2(t=-1,1) {x=t;y=0;} border C3(t=-1,1) {x=-t;y=0;} border C4(t=pi,2pi){x=cos(t); y=sin(t);label=2;} mesh Th1 = buildmesh(C1(n)+C2(… --- ## [What is the maximum PDE dimension that you have seen in a prodution environment?](https://community.freefem.org/t/what-is-the-maximum-pde-dimension-that-you-have-seen-in-a-prodution-environment/2843)
**Author:** [@generator](https://community.freefem.org/u/generator)\ **Replies:** 4\ **Last updated:** [January 4, 2024, 9:10am UTC](https://community.freefem.org/t/what-is-the-maximum-pde-dimension-that-you-have-seen-in-a-prodution-environment/2843 "2024-01-04T09:10:07Z")
Hello, I’m wondering what is the maximum dimension of a PDE engine that you have seen working in a production system ? I mean a realiable system, used every day, with heavy usage from users, etc… thanks --- ## [Record a video with Freefem++ plot](https://community.freefem.org/t/record-a-video-with-freefem-plot/2838)
**Author:** [@lassounon](https://community.freefem.org/u/lassounon)\ **Replies:** 8\ **Last updated:** [January 4, 2024, 8:13am UTC](https://community.freefem.org/t/record-a-video-with-freefem-plot/2838 "2024-01-04T08:13:46Z")
Hello everyone I would like to know if there is a way to edit a video from images like freefem++ does when we display the solution of an evolution equation at each moment. For example I solve a heat equation and with pl… --- ## [Any relation between FF and UFL?](https://community.freefem.org/t/any-relation-between-ff-and-ufl/2863)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 1\ **Last updated:** [January 3, 2024, 8:03am UTC](https://community.freefem.org/t/any-relation-between-ff-and-ufl/2863 "2024-01-03T08:03:06Z")
if you go to page 10 or so there is something called UFL, irksome ufl irksome just curious if anyone is familiar with this and relation to FreeFEM or for that matter Irksome RK lol. Thanks. --- ## [Insight on FreeFem++ Script for American Basket](https://community.freefem.org/t/insight-on-freefem-script-for-american-basket/2846)
**Author:** [@acs](https://community.freefem.org/u/acs)\ **Replies:** 5\ **Last updated:** [January 2, 2024, 10:56am UTC](https://community.freefem.org/t/insight-on-freefem-script-for-american-basket/2846 "2024-01-02T10:56:23Z")
Dear FreeFem++ Community, I am a Finance student exploring the partial differential equation (PDE) approach for pricing American basket options using FreeFem++. I came across a script named “american.edp” and am seeking… --- ## [Coupled reaction diffusion equations](https://community.freefem.org/t/coupled-reaction-diffusion-equations/1626)
**Author:** [@mbletry](https://community.freefem.org/u/mbletry)\ **Replies:** 4\ **Last updated:** [January 1, 2024, 8:26pm UTC](https://community.freefem.org/t/coupled-reaction-diffusion-equations/1626 "2024-01-01T20:26:46Z")
Hello, I am still quite newbie and I am trying to implement a reaction diffusion model which writes: \\partial\_t u=D\_u\\nabla^2 u +u-u^3-v+k \\tau\\partial\_t v=D\_v\\nabla^2 v +u-v where I have to unknowns : u and v. I r… --- ## [Load several functions from one file | split string](https://community.freefem.org/t/load-several-functions-from-one-file-split-string/2853)
**Author:** [@jcvillaquira](https://community.freefem.org/u/jcvillaquira)\ **Replies:** 3\ **Last updated:** [December 28, 2023, 5:41pm UTC](https://community.freefem.org/t/load-several-functions-from-one-file-split-string/2853 "2023-12-28T17:41:25Z")
Hi, this may be a stupid question, but I couldn’t find anything elsewhere. Suppose I have a csv file with a given number of rows, each representing a function. So the something like 0.0,0.0,0.0,0.0 1.0,1.0,1.0,1.0 In… --- ## [Can it solve the coupled PDEs in 3D?](https://community.freefem.org/t/can-it-solve-the-coupled-pdes-in-3d/2849)
**Author:** [@okra](https://community.freefem.org/u/okra)\ **Replies:** 2\ **Last updated:** [December 28, 2023, 3:16am UTC](https://community.freefem.org/t/can-it-solve-the-coupled-pdes-in-3d/2849 "2023-12-28T03:16:27Z")
Hello, everyone! I’m a new learner of FreeFEM, and I need to solve a reaction-diffusion system, which has two variables, just like the following form: u\_t=D11\*(△u)+D12\*(△v)+f(u,v), v\_t=D21\*(△u)+D22\*(△v)+g(u,v), the △ … --- ## [Import and interpolate data.txt](https://community.freefem.org/t/import-and-interpolate-data-txt/2118)
**Author:** [@lassounon](https://community.freefem.org/u/lassounon)\ **Replies:** 6\ **Last updated:** [December 22, 2023, 12:37pm UTC](https://community.freefem.org/t/import-and-interpolate-data-txt/2118 "2023-12-22T12:37:24Z")
Hi, I would like to know how to import and interpolate on my mesh a data (array) of type txt in freefem++. I haven’t seen an example like this in the documentation. Thanks --- ## [Save/load meshL](https://community.freefem.org/t/save-load-meshl/2836)
**Author:** [@ilavi](https://community.freefem.org/u/ilavi)\ **Replies:** 4\ **Last updated:** [December 21, 2023, 3:47pm UTC](https://community.freefem.org/t/save-load-meshl/2836 "2023-12-21T15:47:37Z")
Hi all, What is the proper way of saving and loading a meshL in FreeFem? --- ## [Region and labels in imported mesh](https://community.freefem.org/t/region-and-labels-in-imported-mesh/476)
**Author:** [@hamed](https://community.freefem.org/u/hamed)\ **Replies:** 4\ **Last updated:** [December 21, 2023, 9:28am UTC](https://community.freefem.org/t/region-and-labels-in-imported-mesh/476 "2023-12-21T09:28:01Z")
Hi I made a 3D geometry using GMSH and exported it using .mesh format with it’s Physical entities. load “msh3” load “medit” mesh3 Th = readmesh3(“MCore.mesh”); func co = 1.0\*(region==2); fespace Vh(Th,P0); Vh pco … --- ## [Boundary Conditions of the Edge element](https://community.freefem.org/t/boundary-conditions-of-the-edge-element/2790)
**Author:** [@ksugahar](https://community.freefem.org/u/ksugahar)\ **Replies:** 3\ **Last updated:** [December 18, 2023, 3:32pm UTC](https://community.freefem.org/t/boundary-conditions-of-the-edge-element/2790 "2023-12-18T15:32:59Z")
We are working on a three-dimensional low-frequency electromagnetic problem based on an A-phi formulation as follows. We are using Nedlec elements for vector potentials A and P2 elements for scalar potentials phi. We wo… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=23) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=25)