# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=9 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 10 --- ## [Calculating the heat flux at two boundries](https://community.freefem.org/t/calculating-the-heat-flux-at-two-boundries/3853)
**Author:** [@zhukunw](https://community.freefem.org/u/zhukunw)\ **Replies:** 1\ **Last updated:** [April 17, 2025, 12:13pm UTC](https://community.freefem.org/t/calculating-the-heat-flux-at-two-boundries/3853 "2025-04-17T12:13:00Z")
Hi, I am solving a convection diffusion equation. There are four boundary conditions. I know the right and bottom boundary have no flux condition. Also, the left side looks irregular which denotes the ice water boundary.… --- ## [How to use the Newmark algorithm to solve transient dynamic problems in FreeFEM?](https://community.freefem.org/t/how-to-use-the-newmark-algorithm-to-solve-transient-dynamic-problems-in-freefem/3845)
**Author:** [@AlexanderJFDR](https://community.freefem.org/u/AlexanderJFDR)\ **Replies:** 3\ **Last updated:** [April 17, 2025, 11:59am UTC](https://community.freefem.org/t/how-to-use-the-newmark-algorithm-to-solve-transient-dynamic-problems-in-freefem/3845 "2025-04-17T11:59:57Z")
Hello everyone, I’m currently working on a transient dynamic problem using the Newmark time integration scheme in FreeFEM. While I have carefully implemented the algorithm and double-checked my code multiple times, the … --- ## [Poisson equation with Lagrange multipliers in parallel](https://community.freefem.org/t/poisson-equation-with-lagrange-multipliers-in-parallel/3866)
**Author:** [@maximefio](https://community.freefem.org/u/maximefio)\ **Replies:** 2\ **Last updated:** [April 17, 2025, 5:48am UTC](https://community.freefem.org/t/poisson-equation-with-lagrange-multipliers-in-parallel/3866 "2025-04-17T05:48:09Z")
Hello, I am currently using Freefem to solve a Poisson equation with a source term on an external mesh (contained in ffem-mesh.msh) and the source term is in ffem-drhodt.dat with Lagrange multipliers : include "getARGV… --- ## [Problem in shifting from sequential to parallel](https://community.freefem.org/t/problem-in-shifting-from-sequential-to-parallel/3867)
**Author:** [@sumenchalla](https://community.freefem.org/u/sumenchalla)\ **Replies:** 5\ **Last updated:** [April 17, 2025, 5:12am UTC](https://community.freefem.org/t/problem-in-shifting-from-sequential-to-parallel/3867 "2025-04-17T05:12:15Z")
Dear community members, I’m very new parallel computing, till now I wrote sequential codes, due to time constrain I have to complete my masters by next month end. So I started doing parallel computations. while solving … --- ## [Methods for computing the inverse of large sparse matrix](https://community.freefem.org/t/methods-for-computing-the-inverse-of-large-sparse-matrix/3864)
**Author:** [@Nana](https://community.freefem.org/u/Nana)\ **Replies:** 11\ **Last updated:** [April 16, 2025, 12:05pm UTC](https://community.freefem.org/t/methods-for-computing-the-inverse-of-large-sparse-matrix/3864 "2025-04-16T12:05:33Z")
Dear Freefem users,I developed a set of finite element programs using FreeFEM,within the time-stepping loop, it is necessary to compute the inverse of a large sparse matrix M,Then, the inverse of M is left-multiplied wit… --- ## [A FreeFEM++ code uses the Modified Weak Galerkin Finite Element Method to solve the Poisson Problem](https://community.freefem.org/t/a-freefem-code-uses-the-modified-weak-galerkin-finite-element-method-to-solve-the-poisson-problem/2724)
**Author:** [@ahbabil1983](https://community.freefem.org/u/ahbabil1983)\ **Replies:** 18\ **Last updated:** [April 15, 2025, 3:32am UTC](https://community.freefem.org/t/a-freefem-code-uses-the-modified-weak-galerkin-finite-element-method-to-solve-the-poisson-problem/2724 "2025-04-15T03:32:27Z")
Hello everyone, I wrote a FreeFEM++ code to solve the Poisson Problem -∆u=f in Ω u=g on ∂Ω using the Modified Weak Galerkin Finite Element Method based on the paper: \[1\] “A modified weak Galerkin finite element method”… --- ## [Operator Error in problem formulation](https://community.freefem.org/t/operator-error-in-problem-formulation/3842)
**Author:** [@HMasson](https://community.freefem.org/u/HMasson)\ **Replies:** 3\ **Last updated:** [April 14, 2025, 9:05am UTC](https://community.freefem.org/t/operator-error-in-problem-formulation/3842 "2025-04-14T09:05:52Z")
Hello, I am solving a topology optimization problem using a density method. I need to compute displacements of a 2D linear elastic structure, as well as the solution to the adjoint equation. Below is the code I have b… --- ## [Getting problem to write a flux term codes in DG of Navier-stokes](https://community.freefem.org/t/getting-problem-to-write-a-flux-term-codes-in-dg-of-navier-stokes/3860)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [April 13, 2025, 7:56am UTC](https://community.freefem.org/t/getting-problem-to-write-a-flux-term-codes-in-dg-of-navier-stokes/3860 "2025-04-13T07:56:35Z")
Dear all experts and respected professors, i am getting problem to write the FF++ code of the following flux of F in the FF++: (Getting problem to write second term and third term in FF++ code also third term is non-… --- ## [Traction Forces - BilinearOperator NM error](https://community.freefem.org/t/traction-forces-bilinearoperator-nm-error/3857)
**Author:** [@prayuktha](https://community.freefem.org/u/prayuktha)\ **Replies:** 4\ **Last updated:** [April 12, 2025, 2:40pm UTC](https://community.freefem.org/t/traction-forces-bilinearoperator-nm-error/3857 "2025-04-12T14:40:42Z")
Hi all, I am writing a code to compute the displacement field in Contact Mechanics. But Its giving an error I cant figure out. Can anyone help me? Thanks in Advance. The code is the following one: 1 : load “m… --- ## [Are there good remesh methods in 2D besides extractborder](https://community.freefem.org/t/are-there-good-remesh-methods-in-2d-besides-extractborder/3851)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 5\ **Last updated:** [April 12, 2025, 1:50pm UTC](https://community.freefem.org/t/are-there-good-remesh-methods-in-2d-besides-extractborder/3851 "2025-04-12T13:50:03Z")
I am using ALE method which need to move the mesh and even remesh when it is necessary. I use fixed times remesh before. And now I try to use checkmovemesh to make the remesh more flexible. The latter shows that it can … --- ## [Solution Store for dG set up](https://community.freefem.org/t/solution-store-for-dg-set-up/3850)
**Author:** [@Ravi](https://community.freefem.org/u/Ravi)\ **Replies:** 3\ **Last updated:** [April 11, 2025, 8:49am UTC](https://community.freefem.org/t/solution-store-for-dg-set-up/3850 "2025-04-11T08:49:23Z")
For discontinuous space set up how to store the solution with x and y values in a text file? I tried { ofstream ff(“phi.txt”); ff \<\< phi ; } savemesh(Th,“Th.msh”); and { ofstream ff(“graph.txt”); for (int i … --- ## [How to get external boundary from multiple overlapping meshes?](https://community.freefem.org/t/how-to-get-external-boundary-from-multiple-overlapping-meshes/3855)
**Author:** [@AJMC2002](https://community.freefem.org/u/AJMC2002)\ **Replies:** 0\ **Last updated:** [April 11, 2025, 7:55am UTC](https://community.freefem.org/t/how-to-get-external-boundary-from-multiple-overlapping-meshes/3855 "2025-04-11T07:55:17Z")
I’m generating individual meshes for rectangular pipes (using square(...)) and combining them with +. I’d like to extract the external boundary of the union of these meshes to create a mesh without internal overlaps or d… --- ## [Derivative of P1 function](https://community.freefem.org/t/derivative-of-p1-function/3849)
**Author:** [@Takehiro](https://community.freefem.org/u/Takehiro)\ **Replies:** 3\ **Last updated:** [April 11, 2025, 4:33am UTC](https://community.freefem.org/t/derivative-of-p1-function/3849 "2025-04-11T04:33:57Z")
Dear FreeFem users, I would like to ask please. According to the documentation, mesh Th=square(5,5); fespace Vh(Th,P1); Vh F = x\*x; Vh f = dx(F); then the function f is returned as a P1 function. For example, for no… --- ## [Quadrature formulas in 2D](https://community.freefem.org/t/quadrature-formulas-in-2d/3852)
**Author:** [@ctain](https://community.freefem.org/u/ctain)\ **Replies:** 0\ **Last updated:** [April 10, 2025, 3:15pm UTC](https://community.freefem.org/t/quadrature-formulas-in-2d/3852 "2025-04-10T15:15:46Z")
Hello, I would like to know, if possible, the quadrature formulas used with int2d(Th, qforder = 2) int2d(Th, qforder = 3) int2d(Th, qforder = 6) int2d(Th, qforder = 10) --- ## [Out of memory on Windows 11](https://community.freefem.org/t/out-of-memory-on-windows-11/3844)
**Author:** [@YingShan](https://community.freefem.org/u/YingShan)\ **Replies:** 1\ **Last updated:** [April 10, 2025, 3:03pm UTC](https://community.freefem.org/t/out-of-memory-on-windows-11/3844 "2025-04-10T15:03:35Z")
Hello,why does running FREEFEM++ v4.15 on Windows 11 report “out of memory” when exceeding 2GB, even though my computer has 64GB RAM and a 64-bit system?Can this be solved? --- ## [FreeFem++MPI Error When Loading External Mesh Files .When using FreeFem++MPI to import external mesh files, I encountered the following error](https://community.freefem.org/t/freefem-mpi-error-when-loading-external-mesh-files-when-using-freefem-mpi-to-import-external-mesh-files-i-encountered-the-following-error/3847)
**Author:** [@YingShan](https://community.freefem.org/u/YingShan)\ **Replies:** 1\ **Last updated:** [April 10, 2025, 3:01pm UTC](https://community.freefem.org/t/freefem-mpi-error-when-loading-external-mesh-files-when-using-freefem-mpi-to-import-external-mesh-files-i-encountered-the-following-error/3847 "2025-04-10T15:01:41Z")
Hello everyone, To solve the “Out of Memory” issue in FreeFem++, I started using ​FreeFem++MPI. However, when I import external mesh files into FreeFem++MPI, I encounter the following error: -- Mesh3::Mesh3 Erreur op… --- ## [Periodic conditions boundary](https://community.freefem.org/t/periodic-conditions-boundary/3841)
**Author:** [@taha](https://community.freefem.org/u/taha)\ **Replies:** 5\ **Last updated:** [April 10, 2025, 2:34pm UTC](https://community.freefem.org/t/periodic-conditions-boundary/3841 "2025-04-10T14:34:17Z")
hello everyone, i’m trying to put periodic condition on stokes equation "real Mu = 1.; real pEps = 1.e-10; border C01(t=-0.05, 0.05){x=-1; y=t; label=10;} border C02(t=-1, -0.05){x=t; y=0.05; label=1;} border C03(t=… --- ## [Periodic boundary conditions on Gmsh mesh](https://community.freefem.org/t/periodic-boundary-conditions-on-gmsh-mesh/3413)
**Author:** [@etj](https://community.freefem.org/u/etj)\ **Replies:** 5\ **Last updated:** [April 8, 2025, 2:33pm UTC](https://community.freefem.org/t/periodic-boundary-conditions-on-gmsh-mesh/3413 "2025-04-08T14:33:05Z")
Hello, I am trying to solve a problem with periodic BCs on a pair of opposite faces. The 3D mesh is built with Gmsh. I was careful to have identical 2D meshes on the two faces when building the mesh (using the Gmsh comm… --- ## [Periodic BCs in 3D](https://community.freefem.org/t/periodic-bcs-in-3d/736)
**Author:** [@Alex](https://community.freefem.org/u/Alex)\ **Replies:** 2\ **Last updated:** [April 8, 2025, 12:15pm UTC](https://community.freefem.org/t/periodic-bcs-in-3d/736 "2025-04-08T12:15:21Z")
Hello, I am trying to create a mesh on the parallelepiped (Xmin,Xmax)-by-(Ymin,Ymax)-by-(Zmin,Zmax). The mesh must be uniform in the x- and z-directions, but non-uniform in the y-direction, so I cannot use cube. My appr… --- ## [Lagrange multiplier and Dirichlet boundary condition](https://community.freefem.org/t/lagrange-multiplier-and-dirichlet-boundary-condition/3829)
**Author:** [@Hemanta822](https://community.freefem.org/u/Hemanta822)\ **Replies:** 4\ **Last updated:** [April 5, 2025, 9:33am UTC](https://community.freefem.org/t/lagrange-multiplier-and-dirichlet-boundary-condition/3829 "2025-04-05T09:33:24Z")
Hi all, I am trying to solve poroelasticity in a rectangular domain \[0,1\]\\times\[0,1\]. The four sides are labeled as 1,2,3,4 and at the top boundary \\Gamma (label 4), I have term that includes Lagrange Multiplier as \ **Author:** [@eleckbarraki](https://community.freefem.org/u/eleckbarraki)\ **Replies:** 4\ **Last updated:** [April 4, 2025, 8:56am UTC](https://community.freefem.org/t/poiseuille-flow-simulation-of-viscoplastic-fluid/3811 "2025-04-04T08:56:08Z") Hi all, I’m writing a code to compute the Poiseuille flow of a voscoplastic fluid in the Stokes regime. However it’s giving me an error I can’t figure out. Could anyone help me? the code is the following: load "iovtk… --- ## [Ffglut not available in FreeFEM 4.15](https://community.freefem.org/t/ffglut-not-available-in-freefem-4-15/3826)
**Author:** [@FrancescoB](https://community.freefem.org/u/FrancescoB)\ **Replies:** 1\ **Last updated:** [April 3, 2025, 2:20pm UTC](https://community.freefem.org/t/ffglut-not-available-in-freefem-4-15/3826 "2025-04-03T14:20:52Z")
Dear all, I am running MacOS 15 (Sequoia), and using an M4 Apple Silicon machine. I would just like to report that, to be able to use ffglut with FreeFEM (to display plots or so), I had to install version 4.12. In 4.1… --- ## [Plotting vector field on dense mesh](https://community.freefem.org/t/plotting-vector-field-on-dense-mesh/3832)
**Author:** [@le-tn](https://community.freefem.org/u/le-tn)\ **Replies:** 1\ **Last updated:** [April 3, 2025, 1:38pm UTC](https://community.freefem.org/t/plotting-vector-field-on-dense-mesh/3832 "2025-04-03T13:38:58Z")
Hello everyone, I would like to plot a sparse fraction of the displacements obtained from a dense mesh, so that things can be visualized clearly. How can I proceed? With thanks, tn. --- ## [Getting issues in a simple problem that is based on both elliptic and parabolic type equation](https://community.freefem.org/t/getting-issues-in-a-simple-problem-that-is-based-on-both-elliptic-and-parabolic-type-equation/3828)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 17\ **Last updated:** [April 1, 2025, 12:00pm UTC](https://community.freefem.org/t/getting-issues-in-a-simple-problem-that-is-based-on-both-elliptic-and-parabolic-type-equation/3828 "2025-04-01T12:00:36Z")
Dear all experts and respected professors, i am wondering why the following simple equation does not giving good results\> Deatials pdf of Question\> help.pdf (156.4 KB) ls pdf\> Here, is my codes: Heat\_Elliptic\_com… --- ## [Using Adaptmesh](https://community.freefem.org/t/using-adaptmesh/3822)
**Author:** [@MariamiMamgo](https://community.freefem.org/u/MariamiMamgo)\ **Replies:** 2\ **Last updated:** [April 1, 2025, 9:02am UTC](https://community.freefem.org/t/using-adaptmesh/3822 "2025-04-01T09:02:12Z")
Hello everyone, I’m facing an issue with using Adaptmesh on this type of mesh, it’s not functioning as expected. Could anyone advise me on which parameters of adaptmesh might help resolve this problem? Thank you in adv… --- ## [Adaptive DG FF++ code poisson eqn](https://community.freefem.org/t/adaptive-dg-ff-code-poisson-eqn/3825)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [March 28, 2025, 11:18pm UTC](https://community.freefem.org/t/adaptive-dg-ff-code-poisson-eqn/3825 "2025-03-28T23:18:13Z")
Dear all experts and respected professor, i have tried to write the code of Example 1 and i am trying to verifying the results which are given in the following paper. Numerical Methods Partial - 2019 - Cui - A posterior… --- ## [Use different test functions for different dof](https://community.freefem.org/t/use-different-test-functions-for-different-dof/3824)
**Author:** [@pi.3.141](https://community.freefem.org/u/pi.3.141)\ **Replies:** 3\ **Last updated:** [March 28, 2025, 5:27pm UTC](https://community.freefem.org/t/use-different-test-functions-for-different-dof/3824 "2025-03-28T17:27:57Z")
Dear FreeFem community, I am studying a contact problem, and it turns out that I have to solve a problem, which uses a particular fespace (i.e. different test functions for different dof). More precisely, the problem i… --- ## [Residual based adaptive FreeFem++ code of the Laplace equation (Code is running fine but good results not coming)](https://community.freefem.org/t/residual-based-adaptive-freefem-code-of-the-laplace-equation-code-is-running-fine-but-good-results-not-coming/3815)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 1\ **Last updated:** [March 26, 2025, 8:11am UTC](https://community.freefem.org/t/residual-based-adaptive-freefem-code-of-the-laplace-equation-code-is-running-fine-but-good-results-not-coming/3815 "2025-03-26T08:11:03Z")
Dear all experts, i am trying to compute data oscillations of poisson equation in FreeFem++. Here, is the formula\> ( My doubt is how to compute osc^2(f, \\tau\_h) in FreeFem++ ?? and does last term of (3.2) conta… --- ## [Getting problem in Adaptive Residual based FreeFem++ code of Poisson equation from FreeFem++ doccumentation](https://community.freefem.org/t/getting-problem-in-adaptive-residual-based-freefem-code-of-poisson-equation-from-freefem-doccumentation/3823)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [March 27, 2025, 3:09pm UTC](https://community.freefem.org/t/getting-problem-in-adaptive-residual-based-freefem-code-of-poisson-equation-from-freefem-doccumentation/3823 "2025-03-27T15:09:54Z")
Dear all expert and respected professors, i am wondering why the following adaptive FF++ codes of Poisson equation which i have just taken from the following tutorial of FreeFem++ documentation does not giving good orde… --- ## [Plot a solution restricted to one of the boundary](https://community.freefem.org/t/plot-a-solution-restricted-to-one-of-the-boundary/3757)
**Author:** [@Afrahs](https://community.freefem.org/u/Afrahs)\ **Replies:** 2\ **Last updated:** [March 27, 2025, 9:46am UTC](https://community.freefem.org/t/plot-a-solution-restricted-to-one-of-the-boundary/3757 "2025-03-27T09:46:16Z")
Hi everyone! I’m trying to plot a solution restricted to one of the boundary labels(5) using: meshL bM = extract(G, label=5); But I get an error it seems that meshL is undefined. my FreeFem++ version is 25.3 . How can I… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=8) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=10)