# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=30 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 31 --- ## [How to create a rectangle matrix to link two state vectors about different dof?](https://community.freefem.org/t/how-to-create-a-rectangle-matrix-to-link-two-state-vectors-about-different-dof/2585)
**Author:** [@clthu](https://community.freefem.org/u/clthu)\ **Replies:** 4\ **Last updated:** [July 10, 2023, 4:04am UTC](https://community.freefem.org/t/how-to-create-a-rectangle-matrix-to-link-two-state-vectors-about-different-dof/2585 "2023-07-10T04:04:04Z")
Dear all, These days I met a problem to create the matrx P to link two state vectors q1 and q2, where q1 includes the degree of freedom about the velocity and pressure, while q2 only the degree of freedom about the velo… --- ## [Convolution operator?](https://community.freefem.org/t/convolution-operator/2586)
**Author:** [@sruget](https://community.freefem.org/u/sruget)\ **Replies:** 6\ **Last updated:** [July 9, 2023, 10:06am UTC](https://community.freefem.org/t/convolution-operator/2586 "2023-07-09T10:06:36Z")
Hey everyone, I want to operate a convolution on a function. After a short investigation in the documentation, it appears to me that this was not implemented. I am quite surprise about it. Maybe I am wrong and the conv… --- ## [Problem with UMPACK - VirtualSolverCG.hpp](https://community.freefem.org/t/problem-with-umpack-virtualsolvercg-hpp/2589)
**Author:** [@Loic](https://community.freefem.org/u/Loic)\ **Replies:** 3\ **Last updated:** [July 9, 2023, 6:31am UTC](https://community.freefem.org/t/problem-with-umpack-virtualsolvercg-hpp/2589 "2023-07-09T06:31:12Z")
Dear all, I have a Stiffness matrix and an RHS Matrix, that I solve with : set(StiffGlobal, solver=UMFPACK); xx=StiffGlobal^-1\*RHSGlobal; When I do this in local on my machine, there is no problem. However when I do… --- ## [Creating Animations/ Video of plot](https://community.freefem.org/t/creating-animations-video-of-plot/2580)
**Author:** [@niks9k](https://community.freefem.org/u/niks9k)\ **Replies:** 3\ **Last updated:** [July 8, 2023, 1:25pm UTC](https://community.freefem.org/t/creating-animations-video-of-plot/2580 "2023-07-08T13:25:23Z")
Hi, I was working on a project which in which i had to measure properties of fluid flow, so we ploting the solution to one field variable every 0.01 sec. But for post processing, I needed to create a video or animation o… --- ## [Sommerfeld boundary condition](https://community.freefem.org/t/sommerfeld-boundary-condition/2588)
**Author:** [@jawahar264](https://community.freefem.org/u/jawahar264)\ **Replies:** 0\ **Last updated:** [July 8, 2023, 8:28am UTC](https://community.freefem.org/t/sommerfeld-boundary-condition/2588 "2023-07-08T08:28:56Z")
how to apply Sommerfeld boundary condition in Freefem++? --- ## [Why calculations stop when the plot window is minimized](https://community.freefem.org/t/why-calculations-stop-when-the-plot-window-is-minimized/2587)
**Author:** [@anotherche](https://community.freefem.org/u/anotherche)\ **Replies:** 0\ **Last updated:** [July 7, 2023, 7:59am UTC](https://community.freefem.org/t/why-calculations-stop-when-the-plot-window-is-minimized/2587 "2023-07-07T07:59:05Z")
Hello, everyone! I have been using FreeFem for many years (on Windows) and I am very grateful to the developers for this package! But after all these years, I finally decided to ask about one very annoying feature of Fr… --- ## [Graphics related segfaults possibly solved](https://community.freefem.org/t/graphics-related-segfaults-possibly-solved/2584)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 0\ **Last updated:** [July 5, 2023, 11:13pm UTC](https://community.freefem.org/t/graphics-related-segfaults-possibly-solved/2584 "2023-07-05T23:13:28Z")
I’d seen some other reports of segfaults when plotting FF data. On my earlier Ubuntu Beaver install I had sporadic graphics failures and now with Focal some things reliably created segfaults like “fill=1” in plot. Ear… --- ## [Ciarlet-Raviart for Biharmonic equation, Underconstrained system](https://community.freefem.org/t/ciarlet-raviart-for-biharmonic-equation-underconstrained-system/2582)
**Author:** [@tomgilat](https://community.freefem.org/u/tomgilat)\ **Replies:** 1\ **Last updated:** [July 5, 2023, 12:23pm UTC](https://community.freefem.org/t/ciarlet-raviart-for-biharmonic-equation-underconstrained-system/2582 "2023-07-05T12:23:06Z")
Hi there. I am using FreeFEM++ to solve a biharmonic equation using Ciarlet-Raviart formulation. I want to know what happens if “solve” has an underconstrained system? I am asking because I disregard the fact that one o… --- ## [Error in compilator](https://community.freefem.org/t/error-in-compilator/2570)
**Author:** [@jawahar264](https://community.freefem.org/u/jawahar264)\ **Replies:** 8\ **Last updated:** [July 3, 2023, 9:37am UTC](https://community.freefem.org/t/error-in-compilator/2570 "2023-07-03T09:37:07Z")
load “msh3” load “bem” real k = 10; int n = 100; border circle(t = 0, 2\*pi){x=cos(t); y=sin(t);} meshL ThL = buildmeshL(circle(n)); ThL = OrientNormal(ThL,unbounded=1); BemKernel Ker(“SL”, k=2\*pi); varf vbem(u,v)… --- ## [The output prompt meaning](https://community.freefem.org/t/the-output-prompt-meaning/2575)
**Author:** [@m.lbolok](https://community.freefem.org/u/m.lbolok)\ **Replies:** 1\ **Last updated:** [July 3, 2023, 3:29am UTC](https://community.freefem.org/t/the-output-prompt-meaning/2575 "2023-07-03T03:29:36Z")
Hi, Does anybody know What are the meaning of “Nb pointer”, “memory leak” and “CodeAlloc : nb ptr …, size :…” in the output prompt? Also, what does “######## We forget of deleting” mean? Regards, --- ## [Computing Raviart Thomas function](https://community.freefem.org/t/computing-raviart-thomas-function/2574)
**Author:** [@larismartins](https://community.freefem.org/u/larismartins)\ **Replies:** 0\ **Last updated:** [July 2, 2023, 3:17pm UTC](https://community.freefem.org/t/computing-raviart-thomas-function/2574 "2023-07-02T15:17:02Z")
Hi guys, can someone help me? I’m having a hard time computing the following set of equations: This is the mesh I’m working with: I need to compute the normal component of sigma on all egdes, I tried doing like: f… --- ## [A simple question of PETSc](https://community.freefem.org/t/a-simple-question-of-petsc/2566)
**Author:** [@m31phy](https://community.freefem.org/u/m31phy)\ **Replies:** 4\ **Last updated:** [July 2, 2023, 3:25am UTC](https://community.freefem.org/t/a-simple-question-of-petsc/2566 "2023-07-02T03:25:26Z")
Hello Everyone I have studied FreeFEM++ and its parallelization with lectures in Youtube made by Pierre Jolivet and TuxRiders. During self-studies, I got a simple question but making me slightly confused of. The thing … --- ## [Savesol readsol for P2 FE fields?](https://community.freefem.org/t/savesol-readsol-for-p2-fe-fields/2337)
**Author:** [@plouraboue](https://community.freefem.org/u/plouraboue)\ **Replies:** 6\ **Last updated:** [July 1, 2023, 7:50am UTC](https://community.freefem.org/t/savesol-readsol-for-p2-fe-fields/2337 "2023-07-01T07:50:12Z")
Hi to all, I guess this is a question to Frédéric Hetch or close collaborators : The documentation only describe order=0 and order=1 options for saving a field with savesol and all examples I have seen only do it for P… --- ## [Specify a block preconditioner? KSPSetOperators(KSP ksp, Mat Amat, Mat Pmat)](https://community.freefem.org/t/specify-a-block-preconditioner-kspsetoperators-ksp-ksp-mat-amat-mat-pmat/2567)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 1\ **Last updated:** [June 30, 2023, 5:21am UTC](https://community.freefem.org/t/specify-a-block-preconditioner-kspsetoperators-ksp-ksp-mat-amat-mat-pmat/2567 "2023-06-30T05:21:00Z")
Say Mat A =\[\[UU, UP', UA'\], \[UP, 0, 0\], \[UA, 0, 0\]\]; Mat P=\[\[UU, 0, 0\], \[0, PP, 0\], \[0, 0, AA\]\]; How can we apply P as the preconditioner for solving Ax = f in FreeFem using synt… --- ## [Plotting isovalues in Octave](https://community.freefem.org/t/plotting-isovalues-in-octave/2569)
**Author:** [@galfras](https://community.freefem.org/u/galfras)\ **Replies:** 0\ **Last updated:** [June 29, 2023, 9:06pm UTC](https://community.freefem.org/t/plotting-isovalues-in-octave/2569 "2023-06-29T21:06:58Z")
Hello! I am using Octave to plot a solution using ffmatlib. Is it posible to plot only one isovalue, like the viso does in freefem++? Thanks! --- ## [Discountinous Galerkin example](https://community.freefem.org/t/discountinous-galerkin-example/2559)
**Author:** [@larismartins](https://community.freefem.org/u/larismartins)\ **Replies:** 3\ **Last updated:** [June 28, 2023, 10:18pm UTC](https://community.freefem.org/t/discountinous-galerkin-example/2559 "2023-06-28T22:18:50Z")
Hi everyone, I saw two different ways to compute integral on internal edges and I was wondering which one is the right one. I saw using intalledges(Th)((1-nTonEdge)\*p) and intalledges(Th)(p/nTonEdge); --- ## [Transfer function in](https://community.freefem.org/t/transfer-function-in/2517)
**Author:** [@yhao](https://community.freefem.org/u/yhao)\ **Replies:** 21\ **Last updated:** [June 28, 2023, 1:30pm UTC](https://community.freefem.org/t/transfer-function-in/2517 "2023-06-28T13:30:23Z")
Hi, I am trying to interpolate a scalar field between two different meshes in parallel using transfer function. However, it returns an error. I attached the code here: test.edp (3.5 KB) The first transfer trial would… --- ## [Update only one component in a vector fespace](https://community.freefem.org/t/update-only-one-component-in-a-vector-fespace/2560)
**Author:** [@clthu](https://community.freefem.org/u/clthu)\ **Replies:** 2\ **Last updated:** [June 27, 2023, 12:07pm UTC](https://community.freefem.org/t/update-only-one-component-in-a-vector-fespace/2560 "2023-06-27T12:07:27Z")
Dear all, I met a problem when I tried to update only one component in a vector fespace, for example // fespace Vh(th,\[P2,P2,P1\]) Vh \[ux,uy,z\] // During the calculation, z may become greater than 1, but I want to … --- ## [Wrong matrix indicies for mesh generated by Sphere](https://community.freefem.org/t/wrong-matrix-indicies-for-mesh-generated-by-sphere/2564)
**Author:** [@mhg](https://community.freefem.org/u/mhg)\ **Replies:** 0\ **Last updated:** [June 27, 2023, 9:47am UTC](https://community.freefem.org/t/wrong-matrix-indicies-for-mesh-generated-by-sphere/2564 "2023-06-27T09:47:05Z")
Hello. When I set up a matrix for a surface mesh generated by Sphere with different ansatz and test spaces (e.g. P0 and P1) and then extract the matrix entries, the indices are wrong. See the example in testIJC.edp (91… --- ## [Saving P2 element solution](https://community.freefem.org/t/saving-p2-element-solution/2554)
**Author:** [@niks9k](https://community.freefem.org/u/niks9k)\ **Replies:** 6\ **Last updated:** [June 26, 2023, 6:47pm UTC](https://community.freefem.org/t/saving-p2-element-solution/2554 "2023-06-26T18:47:26Z")
I was working on a project where for the initial part, we were working on P1 element freespace, and saving the solution of our equation with savesol("c1.sol",Th,c,order=1); But later we had to shift to P2 elements, so … --- ## [Parallel computing with PETSc using a large number of cores on a supercomputer](https://community.freefem.org/t/parallel-computing-with-petsc-using-a-large-number-of-cores-on-a-supercomputer/2557)
**Author:** [@Keita](https://community.freefem.org/u/Keita)\ **Replies:** 3\ **Last updated:** [June 25, 2023, 5:24pm UTC](https://community.freefem.org/t/parallel-computing-with-petsc-using-a-large-number-of-cores-on-a-supercomputer/2557 "2023-06-25T17:24:54Z")
Hi FreeFem++ developers! Thank you very much for making FF. I am currently attempting to run FF with PETSc on a supercomputer. Are there any considerations to keep in mind for accuracy when performing large-scale para… --- ## [Interface Freefem++ with C++](https://community.freefem.org/t/interface-freefem-with-c/984)
**Author:** [@Lily](https://community.freefem.org/u/Lily)\ **Replies:** 4\ **Last updated:** [June 22, 2023, 8:19am UTC](https://community.freefem.org/t/interface-freefem-with-c/984 "2023-06-22T08:19:51Z")
Hello users, I have an object-oriented code written in C++ and I would like to call FreeFem to solve a FE problem. So, how can I interface FreeFem with C++ ? I know it’s possible with Python. Is it also possible with C+… --- ## [Updating a matrix for a transient convection problem without using convect()](https://community.freefem.org/t/updating-a-matrix-for-a-transient-convection-problem-without-using-convect/2550)
**Author:** [@sbreckling](https://community.freefem.org/u/sbreckling)\ **Replies:** 0\ **Last updated:** [June 21, 2023, 1:42am UTC](https://community.freefem.org/t/updating-a-matrix-for-a-transient-convection-problem-without-using-convect/2550 "2023-06-21T01:42:18Z")
I am having difficulty updating the LHS of my problem of the form L(u,v) + N(\\bar{u},u,v) = f where L is linear, N is not such that \\bar{u} = F(u) (for some F) and is linearized by either iterating or otherwise. (In t… --- ## [Lagrange multiplier for Dirichlet boundary condition](https://community.freefem.org/t/lagrange-multiplier-for-dirichlet-boundary-condition/2402)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 30\ **Last updated:** [June 21, 2023, 4:06pm UTC](https://community.freefem.org/t/lagrange-multiplier-for-dirichlet-boundary-condition/2402 "2023-06-21T16:06:12Z")
Dear all, Is there an example to implement Dirichlet boundary condition using Lagrange multiplier method? Thank you in advance! Best, Yongxing --- ## [Representaion d'une fonction](https://community.freefem.org/t/representaion-dune-fonction/2547)
**Author:** [@Leonidas](https://community.freefem.org/u/Leonidas)\ **Replies:** 3\ **Last updated:** [June 21, 2023, 7:06am UTC](https://community.freefem.org/t/representaion-dune-fonction/2547 "2023-06-21T07:06:45Z")
Bonjour, J’aimerai savoir comment représenter une fonction f(x) en fonction de x dans Freefem? Pour une fonction dépendant de deux variables f(x, t) comment représenter cette fonction f en fonction de x et de t ? Merci… --- ## [Global computation of an error with PETSc using block matrices](https://community.freefem.org/t/global-computation-of-an-error-with-petsc-using-block-matrices/2549)
**Author:** [@AzizTakhirov](https://community.freefem.org/u/AzizTakhirov)\ **Replies:** 2\ **Last updated:** [June 19, 2023, 6:10pm UTC](https://community.freefem.org/t/global-computation-of-an-error-with-petsc-using-block-matrices/2549 "2023-06-19T18:10:22Z")
Hello, I’ve adapted the part of the stokes-block-2d-PETSc,edp to conduct a convergence test with a manufactured solution. I need to have tgv=-1. The code works out OK, including the plots, but the errors are almost sta… --- ## [The meaning of "Nb pointer", "memory leak" and "CodeAlloc"](https://community.freefem.org/t/the-meaning-of-nb-pointer-memory-leak-and-codealloc/2548)
**Author:** [@m.lbolok](https://community.freefem.org/u/m.lbolok)\ **Replies:** 0\ **Last updated:** [June 17, 2023, 4:12pm UTC](https://community.freefem.org/t/the-meaning-of-nb-pointer-memory-leak-and-codealloc/2548 "2023-06-17T16:12:12Z")
Hi, What is the meaning of “Nb pointer”, “memory leak” and “CodeAlloc : nb ptr …, size :…” in the output prompt? Also, what does “######## We forget of deleting” mean? Regards, --- ## [Writing non-ascii or binary data to ofstream?](https://community.freefem.org/t/writing-non-ascii-or-binary-data-to-ofstream/2545)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 2\ **Last updated:** [June 16, 2023, 4:42pm UTC](https://community.freefem.org/t/writing-non-ascii-or-binary-data-to-ofstream/2545 "2023-06-16T16:42:55Z")
I can’t find anyway to write a simple “0” or other char to ofstream. Syntax highligher colors “char” but it is not accepted by FF. I and adding “binary” to the ofstream ctor does nothing afaict. Thanks. --- ## [Pass array value by reference in function definition](https://community.freefem.org/t/pass-array-value-by-reference-in-function-definition/2546)
**Author:** [@m.lbolok](https://community.freefem.org/u/m.lbolok)\ **Replies:** 2\ **Last updated:** [June 16, 2023, 10:32am UTC](https://community.freefem.org/t/pass-array-value-by-reference-in-function-definition/2546 "2023-06-16T10:32:43Z")
Hi, I would like to pass an array by reference in a function. I have tried this: func real myfunc2(real a,real b,real\[int\] &c(2)) { c(0)=a+b; c(1)=a-b; return 0.; } But it does not work. Is there any way to pass … --- ## [Fonction getARG](https://community.freefem.org/t/fonction-getarg/2543)
**Author:** [@aweni](https://community.freefem.org/u/aweni)\ **Replies:** 1\ **Last updated:** [June 15, 2023, 7:28am UTC](https://community.freefem.org/t/fonction-getarg/2543 "2023-06-15T07:28:32Z")
Bonsoir à tous j’aimerais savoir comment utilisé la fonction getARG et comment etre que le code prends pas mal les paramètres. [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=29) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=31)