# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=19 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 20 --- ## [GMRES iteration options](https://community.freefem.org/t/gmres-iteration-options/3202)
**Author:** [@Alexei](https://community.freefem.org/u/Alexei)\ **Replies:** 7\ **Last updated:** [May 22, 2024, 5:31am UTC](https://community.freefem.org/t/gmres-iteration-options/3202 "2024-05-22T05:31:30Z")
Dear All, I would like to control the maximal number of iteration steps/absolute tolerance for the GMRES algorithm, but I couldn’t find the correct options. Thanks a lot for information, Alexei --- ## [Criss Cross triangulation](https://community.freefem.org/t/criss-cross-triangulation/3254)
**Author:** [@GGian](https://community.freefem.org/u/GGian)\ **Replies:** 4\ **Last updated:** [May 20, 2024, 8:55am UTC](https://community.freefem.org/t/criss-cross-triangulation/3254 "2024-05-20T08:55:12Z")
Hello, I would like to do some calculations on the unit square using criss-cross meshes. Is there a simple way to create such a mesh on a unit square? Thanks! --- ## [Solver Selection](https://community.freefem.org/t/solver-selection/3251)
**Author:** [@Walid](https://community.freefem.org/u/Walid)\ **Replies:** 4\ **Last updated:** [May 17, 2024, 6:04pm UTC](https://community.freefem.org/t/solver-selection/3251 "2024-05-17T18:04:50Z")
Hello All, I have a basic question and looking forward have an answer or a guide How to choose the correct solver for a problem ? or how to decide if I should use MUMPS or PETSc or other plugin the problem I am tryin… --- ## [Linking a 3rd party library](https://community.freefem.org/t/linking-a-3rd-party-library/1313)
**Author:** [@Markov](https://community.freefem.org/u/Markov)\ **Replies:** 7\ **Last updated:** [May 16, 2024, 10:39am UTC](https://community.freefem.org/t/linking-a-3rd-party-library/1313 "2024-05-16T10:39:47Z")
Hello everyone, I am trying to link a 3rd party library in FreeFem++ called cwipi, the library in coded in C++. I changed the pref file to link the .so and the .h files but it did not work (I can load the library but I … --- ## [Behavior of varf with rhs and on()](https://community.freefem.org/t/behavior-of-varf-with-rhs-and-on/3248)
**Author:** [@fb77](https://community.freefem.org/u/fb77)\ **Replies:** 11\ **Last updated:** [May 15, 2024, 5:04pm UTC](https://community.freefem.org/t/behavior-of-varf-with-rhs-and-on/3248 "2024-05-15T17:04:12Z")
Can anyone comment on the extraction of the linear part in varf() ? There is an issue of sign, it seems that it is treated differently depending if it is an integral source or an on() boundary condition. The simple code … --- ## [Too many vertices when I apply the adaptmesh comand](https://community.freefem.org/t/too-many-vertices-when-i-apply-the-adaptmesh-comand/2030)
**Author:** [@Jacoban90](https://community.freefem.org/u/Jacoban90)\ **Replies:** 2\ **Last updated:** [May 14, 2024, 12:23pm UTC](https://community.freefem.org/t/too-many-vertices-when-i-apply-the-adaptmesh-comand/2030 "2024-05-14T12:23:35Z")
Hello Freefem Users, I’ve been trying to simulate iteratively a deformation of a rectangular geometry and readapting the mesh in order to avoid execution errors. However, I after a few iteration I still obtain an error … --- ## [A question about mesh adaptation](https://community.freefem.org/t/a-question-about-mesh-adaptation/3242)
**Author:** [@jna1g18](https://community.freefem.org/u/jna1g18)\ **Replies:** 0\ **Last updated:** [May 13, 2024, 4:48pm UTC](https://community.freefem.org/t/a-question-about-mesh-adaptation/3242 "2024-05-13T16:48:47Z")
Hi, can someone explain to me exactly what the parameter err does in the function adaptmesh? I know that it is a measure of error and that it controls the accuracy of the interpolated function, but I’d like a little more… --- ## [How to implementthe penalty FEM for solving the steady stokes equations](https://community.freefem.org/t/how-to-implementthe-penalty-fem-for-solving-the-steady-stokes-equations/3236)
**Author:** [@hanweiwei](https://community.freefem.org/u/hanweiwei)\ **Replies:** 2\ **Last updated:** [May 11, 2024, 11:55pm UTC](https://community.freefem.org/t/how-to-implementthe-penalty-fem-for-solving-the-steady-stokes-equations/3236 "2024-05-11T23:55:16Z")
Hello everyone, When using the penalty method for solving Stokes equation, we can decouple the computation of velocity field with the pressure. But how to implement projection operator? --- ## [Adaptmesh is not deterministic](https://community.freefem.org/t/adaptmesh-is-not-deterministic/3237)
**Author:** [@clthu](https://community.freefem.org/u/clthu)\ **Replies:** 0\ **Last updated:** [May 11, 2024, 8:48am UTC](https://community.freefem.org/t/adaptmesh-is-not-deterministic/3237 "2024-05-11T08:48:47Z")
Dear all, I found in sometimes the adaptmesh will not give the same results. The mesh adapted with the same adaptfields and options may be a little different in the number of vertices ( although not big difference , lik… --- ## [Nédéléc edge element](https://community.freefem.org/t/nedelec-edge-element/3235)
**Author:** [@LXX](https://community.freefem.org/u/LXX)\ **Replies:** 0\ **Last updated:** [May 10, 2024, 11:51am UTC](https://community.freefem.org/t/nedelec-edge-element/3235 "2024-05-10T11:51:42Z")
I am trying to implement a method for solving MHD equations in 2D or 3D using the first family second-order H(curl)-conforming Nédéléc edge element for magnetic. However, in the source code, it seems like only type 1… --- ## [About intalledges and internal edges](https://community.freefem.org/t/about-intalledges-and-internal-edges/3231)
**Author:** [@Aubium](https://community.freefem.org/u/Aubium)\ **Replies:** 2\ **Last updated:** [May 9, 2024, 11:26am UTC](https://community.freefem.org/t/about-intalledges-and-internal-edges/3231 "2024-05-09T11:26:38Z")
Greetings fellow members, As its name suggests, intalledges integrates on all edges (interior and boundary alike). Then how to integrate on internal edges only ? Best regards. --- ## [Bad accuracy of eigenvalue, how solve it?](https://community.freefem.org/t/bad-accuracy-of-eigenvalue-how-solve-it/3232)
**Author:** [@bcaval](https://community.freefem.org/u/bcaval)\ **Replies:** 0\ **Last updated:** [May 8, 2024, 3:46pm UTC](https://community.freefem.org/t/bad-accuracy-of-eigenvalue-how-solve-it/3232 "2024-05-08T15:46:20Z")
Dear freefem community, Could you help me to understand my mistake or to advise me the best way in freefem++ today to make a sure eigenvalue solving ? Indeed I would like like to make eigenvalue analysis for thermoelas… --- ## [Memory Leak on MacOS with ff-mpirun](https://community.freefem.org/t/memory-leak-on-macos-with-ff-mpirun/3154)
**Author:** [@LXX](https://community.freefem.org/u/LXX)\ **Replies:** 8\ **Last updated:** [May 8, 2024, 12:16pm UTC](https://community.freefem.org/t/memory-leak-on-macos-with-ff-mpirun/3154 "2024-05-08T12:16:57Z")
Hello, everyone. Firstly, I install open-mai on MacOS. mpirun (Open MPI) 5.0.3 For diffusion-2d.edp When I use ff-mpirun -np 4 diffusion-2d.edp Warning: -- Your set of boundary condition is incompatible with the me… --- ## [2d Integration over a 2d domain](https://community.freefem.org/t/2d-integration-over-a-2d-domain/3229)
**Author:** [@Walid](https://community.freefem.org/u/Walid)\ **Replies:** 0\ **Last updated:** [May 7, 2024, 8:45pm UTC](https://community.freefem.org/t/2d-integration-over-a-2d-domain/3229 "2024-05-07T20:45:34Z")
Hello all, I need you support to calculate I = (1/V) ∬ 2πqr(µe.We+µp.Wp+µn.Wn) EL drdz where We,n,p and µe, and El are finite element functions and µn, p are real numbers VE EL; Ve Ne, Neold; Ve Np, Npold; Ve Nn,… --- ## [Ph or ? for anisotropic property by region](https://community.freefem.org/t/ph-or-for-anisotropic-property-by-region/3227)
**Author:** [@bcaval](https://community.freefem.org/u/bcaval)\ **Replies:** 0\ **Last updated:** [May 7, 2024, 9:58am UTC](https://community.freefem.org/t/ph-or-for-anisotropic-property-by-region/3227 "2024-05-07T09:58:01Z")
Dear freefem community, I would like to have your advices for the best implementation of anisotropic physical property for each material. In fact I imagine this for attributing physical property to each material, see b… --- ## [Boundary condition in eigenvalue problem](https://community.freefem.org/t/boundary-condition-in-eigenvalue-problem/3179)
**Author:** [@maximefio](https://community.freefem.org/u/maximefio)\ **Replies:** 14\ **Last updated:** [May 6, 2024, 5:16pm UTC](https://community.freefem.org/t/boundary-condition-in-eigenvalue-problem/3179 "2024-05-06T17:16:38Z")
Hello, I am currently trying to do the linear stability around a sphere flow at low Reynolds number (following the work of P. Meliga, J.-M.Chomaz and D.Sippa ( Unsteadiness in the wake of disks and spheres: Instability,… --- ## [How implement ON for an identity matrix?](https://community.freefem.org/t/how-implement-on-for-an-identity-matrix/3208)
**Author:** [@bcaval](https://community.freefem.org/u/bcaval)\ **Replies:** 1\ **Last updated:** [May 5, 2024, 12:28pm UTC](https://community.freefem.org/t/how-implement-on-for-an-identity-matrix/3208 "2024-05-05T12:28:45Z")
Dear freefem community, I try to extract complex eigenvalue for a problem like M X" + C X’ + K X = 0. It yields to a block matrix like : AG \* \[X, X’\] = lambda\* BG\* \[X,X’\] so that… matrix mKK,AG,BG; mKK = (-1)\*KK; A… --- ## [Array of vectorial fespace function](https://community.freefem.org/t/array-of-vectorial-fespace-function/3222)
**Author:** [@clthu](https://community.freefem.org/u/clthu)\ **Replies:** 1\ **Last updated:** [May 5, 2024, 6:37am UTC](https://community.freefem.org/t/array-of-vectorial-fespace-function/3222 "2024-05-05T06:37:32Z")
Dear all, I am trying to make an array of vectorial fespace funciton like this: macro defU(u) \[u#x,u#y,u#z\]; XXXh defU(uq1); XXXh\[int\] defU(uq)(10); and after solving the uq1, I want to restore uq1 to the first arr… --- ## [How i include the ffmathlib Commnad on FreeFem++ data](https://community.freefem.org/t/how-i-include-the-ffmathlib-commnad-on-freefem-data/3218)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 1\ **Last updated:** [May 5, 2024, 6:27am UTC](https://community.freefem.org/t/how-i-include-the-ffmathlib-commnad-on-freefem-data/3218 "2024-05-05T06:27:41Z")
Can you tell me how i include ffmatlib command to FreeFem++ codes. According to the online doccumentation of FreeFem++, i have included it but it showing error. Whether i have to install some packages for it. matlab\_oct… --- ## [How to find the determinant or condition number of the stiffness matrix?](https://community.freefem.org/t/how-to-find-the-determinant-or-condition-number-of-the-stiffness-matrix/1506)
**Author:** [@Qianrui](https://community.freefem.org/u/Qianrui)\ **Replies:** 21\ **Last updated:** [May 5, 2024, 6:00am UTC](https://community.freefem.org/t/how-to-find-the-determinant-or-condition-number-of-the-stiffness-matrix/1506 "2024-05-05T06:00:04Z")
Hi,profeesor How to find the determinant or condition number of the stiffness matrix? --- ## [Big overhead when using MPI](https://community.freefem.org/t/big-overhead-when-using-mpi/3211)
**Author:** [@jcvillaquira](https://community.freefem.org/u/jcvillaquira)\ **Replies:** 5\ **Last updated:** [May 5, 2024, 5:59am UTC](https://community.freefem.org/t/big-overhead-when-using-mpi/3211 "2024-05-05T05:59:05Z")
Hi, I am coding a project in which I need to call a FF++ script multiple times. This is script is parallelized (and this saves a lot of time) but there is a big overhead. As a mwe, when running a single script with one … --- ## [Implementation of Linear Programming with IPOPT](https://community.freefem.org/t/implementation-of-linear-programming-with-ipopt/887)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 3\ **Last updated:** [May 4, 2024, 4:45pm UTC](https://community.freefem.org/t/implementation-of-linear-programming-with-ipopt/887 "2024-05-04T16:45:20Z")
Hello, I try to use IPOPT to minimize a linear function under some bound constraints. According to the doc the following code should work: load "ff-Ipopt" real\[int\] a = \[-1.0,-1.2\]; real\[int\] UB = \[1.0,1.0\]; real\[int\]… --- ## [Non-zero dirichlet BC on Stokes Eigenvalue problem](https://community.freefem.org/t/non-zero-dirichlet-bc-on-stokes-eigenvalue-problem/3209)
**Author:** [@djahid](https://community.freefem.org/u/djahid)\ **Replies:** 1\ **Last updated:** [May 4, 2024, 6:59am UTC](https://community.freefem.org/t/non-zero-dirichlet-bc-on-stokes-eigenvalue-problem/3209 "2024-05-04T06:59:09Z")
Hello, I’m having trouble trying to impose non-zero boundary conditions on the Stokes Eigenvalue problem using the on() function. The solution is always the same no matter what values I set the Ux and Uy variables in t… --- ## [Adaptmesh chaging boundary labels](https://community.freefem.org/t/adaptmesh-chaging-boundary-labels/3201)
**Author:** [@larismartins](https://community.freefem.org/u/larismartins)\ **Replies:** 6\ **Last updated:** [May 3, 2024, 5:03pm UTC](https://community.freefem.org/t/adaptmesh-chaging-boundary-labels/3201 "2024-05-03T17:03:20Z")
Hello everyone, I have a mesh resulting from adaptmesh function, now, I’m trying to use this mesh to solve a new problem, however, my problem has neumann and non homogeneous dirichlet boundary conditions and the solutio… --- ## [Boundary conditions on loaded mesh](https://community.freefem.org/t/boundary-conditions-on-loaded-mesh/3207)
**Author:** [@Dakyn](https://community.freefem.org/u/Dakyn)\ **Replies:** 0\ **Last updated:** [May 2, 2024, 5:47pm UTC](https://community.freefem.org/t/boundary-conditions-on-loaded-mesh/3207 "2024-05-02T17:47:28Z")
Dear Community, I am struggling with the problem of how to properly set the boundary conditions for the Poisson equation on my loaded mesh. I’ve tried several options, but usually my calculation always stops at one valu… --- ## [Avoid compilation, mesh reading, etc. when executing script multiple times](https://community.freefem.org/t/avoid-compilation-mesh-reading-etc-when-executing-script-multiple-times/3206)
**Author:** [@jcvillaquira](https://community.freefem.org/u/jcvillaquira)\ **Replies:** 1\ **Last updated:** [May 2, 2024, 3:44pm UTC](https://community.freefem.org/t/avoid-compilation-mesh-reading-etc-when-executing-script-multiple-times/3206 "2024-05-02T15:44:46Z")
Hi, I have a FF++ script which solves a boundary value problem based on some inputs that can be passed as parameters p1, p2, . . . , pn when executing it. These parameters are generated in other code parts written in an… --- ## [A good reference on Discontinuous Galerkin](https://community.freefem.org/t/a-good-reference-on-discontinuous-galerkin/3203)
**Author:** [@Aubium](https://community.freefem.org/u/Aubium)\ **Replies:** 0\ **Last updated:** [May 2, 2024, 12:59pm UTC](https://community.freefem.org/t/a-good-reference-on-discontinuous-galerkin/3203 "2024-05-02T12:59:13Z")
Greeting fellow members, I’m looking for a solid reference regarding Discontinuous Galerkin, how to derive DG-schemes with applications to further grasp the method. Thank you, and good luck. --- ## [Error loading PETSC-complex](https://community.freefem.org/t/error-loading-petsc-complex/3182)
**Author:** [@bcaval](https://community.freefem.org/u/bcaval)\ **Replies:** 0\ **Last updated:** [April 30, 2024, 6:48pm UTC](https://community.freefem.org/t/error-loading-petsc-complex/3182 "2024-04-30T18:48:12Z")
Hello Freefem community, I have an error message, as I just load “PETSC-complex”, I have installed the last version on windows 64. No problem with load “PETSc” but for the complex it is : fail: list prefix: 'C:\\Progra… --- ## [EigenValue function](https://community.freefem.org/t/eigenvalue-function/3180)
**Author:** [@maximefio](https://community.freefem.org/u/maximefio)\ **Replies:** 0\ **Last updated:** [April 30, 2024, 1:06pm UTC](https://community.freefem.org/t/eigenvalue-function/3180 "2024-04-30T13:06:21Z")
Hello, I am currently trying to solve an eigenvalue problem with the function EigenValue of Freefem++ and when the code start to launch this function, I get such kind of error: Assertion fail : ((!this-\>N() || !this-\>M… --- ## [Wrong answer from imposing a point value for the pressure via the penalty method](https://community.freefem.org/t/wrong-answer-from-imposing-a-point-value-for-the-pressure-via-the-penalty-method/3176)
**Author:** [@ars\_cn](https://community.freefem.org/u/ars_cn)\ **Replies:** 0\ **Last updated:** [April 30, 2024, 2:58am UTC](https://community.freefem.org/t/wrong-answer-from-imposing-a-point-value-for-the-pressure-via-the-penalty-method/3176 "2024-04-30T02:58:15Z")
Hello, I am working on the Stokes equation now. I noticed FreeFEM introduces an extra small L2 term on the pressure to stabilize the scheme. However, I am trying to impose the pressure with a point value to gain the wel… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=18) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=20)