# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=75 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 76 --- ## [Solutions of generalized Poisson's equation on a 3D surface](https://community.freefem.org/t/solutions-of-generalized-poissons-equation-on-a-3d-surface/100)
**Author:** [@Bob\_IDP](https://community.freefem.org/u/Bob_IDP)\ **Replies:** 1\ **Last updated:** [July 30, 2019, 4:01pm UTC](https://community.freefem.org/t/solutions-of-generalized-poissons-equation-on-a-3d-surface/100 "2019-07-30T16:01:51Z")
I have been solving the potential in a thin resistive film with electrodes on the surface of a cylinder by unwrapping it to a flat 2D problem and solving the generalized Poisson’s equation with a finite difference algori… --- ## [Integrate FreeFem in a software](https://community.freefem.org/t/integrate-freefem-in-a-software/96)
**Author:** [@nicomobile](https://community.freefem.org/u/nicomobile)\ **Replies:** 1\ **Last updated:** [July 29, 2019, 1:21pm UTC](https://community.freefem.org/t/integrate-freefem-in-a-software/96 "2019-07-29T13:21:41Z")
Hello, I have been coding softwares since 5 years now, mostly with Windev (pcsoft) coding platform that allows great speed for coding and convinient tools to make software. Mostly I do bridge design softwares and also … --- ## [A problem of parallel computation in 3D](https://community.freefem.org/t/a-problem-of-parallel-computation-in-3d/95)
**Author:** [@zhaog6](https://community.freefem.org/u/zhaog6)\ **Replies:** 0\ **Last updated:** [July 15, 2019, 3:09am UTC](https://community.freefem.org/t/a-problem-of-parallel-computation-in-3d/95 "2019-07-15T03:09:51Z")
Dear all, There are two questions about FreeFem++. I would like to ask if FreeFem++ supports distributed three-dimensional structured or unstructured mesh used in parallel computation? we may involve in adaptation re… --- ## [Change in parsing macro since v4?](https://community.freefem.org/t/change-in-parsing-macro-since-v4/92)
**Author:** [@arousta](https://community.freefem.org/u/arousta)\ **Replies:** 1\ **Last updated:** [July 10, 2019, 3:59pm UTC](https://community.freefem.org/t/change-in-parsing-macro-since-v4/92 "2019-07-10T15:59:02Z")
Blockquote macro DEFArr(space) real\[int\] space#Arr(space#.ndof); // mesh Th = square(10,10,flags=3); fespace Lh(Th,P0); DEF(Lh) The above code used to be fine on older versions. Now on v4.2 I get error: 2 : rea… --- ## [Problem of using parms solver](https://community.freefem.org/t/problem-of-using-parms-solver/93)
**Author:** [@xlzheng](https://community.freefem.org/u/xlzheng)\ **Replies:** 0\ **Last updated:** [July 10, 2019, 9:29am UTC](https://community.freefem.org/t/problem-of-using-parms-solver/93 "2019-07-10T09:29:24Z")
I want to use the parallel sparse iterative solver: pARMS, but when I run the example, I get " Exec error : Plugins parms\_FreeFem is remove" but under the path : /plugin/mpi/ , parms\_FreeFem.cpp、parms\_FreeFem.o、parm… --- ## [About new sparse matrix structure](https://community.freefem.org/t/about-new-sparse-matrix-structure/88)
**Author:** [@e-aranda](https://community.freefem.org/u/e-aranda)\ **Replies:** 5\ **Last updated:** [July 4, 2019, 2:52pm UTC](https://community.freefem.org/t/about-new-sparse-matrix-structure/88 "2019-07-04T14:52:51Z")
I had a c++ code linked with FreeFem version 3, in which I built a matrix using MatriceMorse\ \* ret = new MatriceMorse\(np,np,newnnz,false,newa,newlg,newcl); However, in version 4, I get: error: no match… --- ## [Assemble finite element matrix without varf](https://community.freefem.org/t/assemble-finite-element-matrix-without-varf/82)
**Author:** [@Alexandre](https://community.freefem.org/u/Alexandre)\ **Replies:** 3\ **Last updated:** [June 28, 2019, 8:37am UTC](https://community.freefem.org/t/assemble-finite-element-matrix-without-varf/82 "2019-06-28T08:37:00Z")
Dear all, I am trying to assemble a finite element matrix with “custom” local submatrices. The pseudo-code is the following: // For each element for (int i=0;i\ **Author:** [@Hugo](https://community.freefem.org/u/Hugo)\ **Replies:** 0\ **Last updated:** [June 26, 2019, 9:55am UTC](https://community.freefem.org/t/computing-normal-heat-flux-density/86 "2019-06-26T09:55:13Z") Dear all, I’m currently working on a thermic problem (Laplace equation) and i want to compute the normal heat flux density along the borders. I tried to compute it with a variationnal form, like this: qx = -khdx(u); /… --- ## [Controle optimale](https://community.freefem.org/t/controle-optimale/84)
**Author:** [@Ilyan](https://community.freefem.org/u/Ilyan)\ **Replies:** 0\ **Last updated:** [June 25, 2019, 4:45pm UTC](https://community.freefem.org/t/controle-optimale/84 "2019-06-25T16:45:41Z")
Bonjour, Puis je savoir comment on procéde au controle optimale dans le cas non-stationnaire avec terme source (source de chaleur, polluant, …). En utilisant : Systeme direct Adjoint J et ∇J Si quelqu’un parmi vous … --- ## [Wave equation in FREEFEM](https://community.freefem.org/t/wave-equation-in-freefem/77)
**Author:** [@abuAnat](https://community.freefem.org/u/abuAnat)\ **Replies:** 1\ **Last updated:** [June 19, 2019, 11:50am UTC](https://community.freefem.org/t/wave-equation-in-freefem/77 "2019-06-19T11:50:27Z")
Specific FEM software work better for some kind of PDE than others; is FREEFEM appropriate for solving Hyperbolic problems like time-domain wave equations? --- ## [How to implement a thermal ramp ISO834 in convection-radiation code](https://community.freefem.org/t/how-to-implement-a-thermal-ramp-iso834-in-convection-radiation-code/74)
**Author:** [@fffm\_84](https://community.freefem.org/u/fffm_84)\ **Replies:** 2\ **Last updated:** [June 15, 2019, 12:11pm UTC](https://community.freefem.org/t/how-to-implement-a-thermal-ramp-iso834-in-convection-radiation-code/74 "2019-06-15T12:11:34Z")
My problem is to implement a thermal ramp ISO834 in convection-radiation code (FreeFem++) for Fourier’s problem. I want to obtain a thermal map for a concrete square section, applying the ISO834 ramp to the 4 side bound… --- ## [Type of surface element](https://community.freefem.org/t/type-of-surface-element/72)
**Author:** [@agTSL](https://community.freefem.org/u/agTSL)\ **Replies:** 2\ **Last updated:** [June 13, 2019, 8:01am UTC](https://community.freefem.org/t/type-of-surface-element/72 "2019-06-13T08:01:00Z")
Hi, I would like to use surface element which are new in v4.2.1. What are the types of these elements? During the freefem day in 2018, I writed that was P1S, but it doesn’t work. Best Regards Alexandre --- ## [Max of an solution](https://community.freefem.org/t/max-of-an-solution/64)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 1\ **Last updated:** [June 10, 2019, 9:23am UTC](https://community.freefem.org/t/max-of-an-solution/64 "2019-06-10T09:23:35Z")
Hi, how we calculate the maximum of an solution uh with freefem++: max uh Kind regards --- ## [Computing the divergence of the normal vector](https://community.freefem.org/t/computing-the-divergence-of-the-normal-vector/68)
**Author:** [@sarahf](https://community.freefem.org/u/sarahf)\ **Replies:** 0\ **Last updated:** [June 5, 2019, 8:36am UTC](https://community.freefem.org/t/computing-the-divergence-of-the-normal-vector/68 "2019-06-05T08:36:56Z")
Dear all, I want to compute the shape derivative of a form and hence i need to solve a problem with int1d(Th)( f (dx(N.x)+dy(N.y)) )\*. This does not work as such, and since I am optimizing my shape, I don’t have an exp… --- ## [Error of two solutions](https://community.freefem.org/t/error-of-two-solutions/63)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [May 30, 2019, 6:42pm UTC](https://community.freefem.org/t/error-of-two-solutions/63 "2019-05-30T18:42:51Z")
Hi, i have to calculate in 3D solutions u and w of two problems: du/dt - \\Delta u = f and dw/dt - Delta w +w =f , (x,y,z) \\in (0,1)^3, t \\in \[0,1\] where f(x,y,z)= 0.25\*sin(2\*pi\*x) and calculate the norme H^1 of the … --- ## [Error - saving and loading 3D meshes](https://community.freefem.org/t/error-saving-and-loading-3d-meshes/61)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 1\ **Last updated:** [May 28, 2019, 9:11pm UTC](https://community.freefem.org/t/error-saving-and-loading-3d-meshes/61 "2019-05-28T21:11:26Z")
Hello, Using version 4.1 I did not manage to run a code which ran well previously (before 4.0). The idea is that I take a 3D mesh and use the trunc function in order to construct two meshes. Then I save them, but I cann… --- ## [Eigenvalue problem with several domains](https://community.freefem.org/t/eigenvalue-problem-with-several-domains/60)
**Author:** [@GaelleB](https://community.freefem.org/u/GaelleB)\ **Replies:** 0\ **Last updated:** [May 28, 2019, 10:29am UTC](https://community.freefem.org/t/eigenvalue-problem-with-several-domains/60 "2019-05-28T10:29:55Z")
Hello, I solved an eigenvalue problem on a domain D= D1 U D2 using the matrix construction as explained in the Freefem documentation. Each domain is triangulated and the meshes are adapted with the corresponding metric.… --- ## [Plot in 3d with .vtu (visualization with paraview)](https://community.freefem.org/t/plot-in-3d-with-vtu-visualization-with-paraview/58)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 1\ **Last updated:** [May 27, 2019, 5:29pm UTC](https://community.freefem.org/t/plot-in-3d-with-vtu-visualization-with-paraview/58 "2019-05-27T17:29:33Z")
Hi i have to plot the Following function: q(x/eps,y/eps,z/eps)=1 if (x/eps,y/eps,z/eps) \\in B\_{\\delta}+ Z^3, else 0. where B\_{delta} is the ball with radius \\delta= ((3/4)(1/(wpi)))^{1/3} we choise eps=0.1 and w=200… --- ## [Plot in 3d with .vtu and paraview](https://community.freefem.org/t/plot-in-3d-with-vtu-and-paraview/57)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [May 24, 2019, 5:35pm UTC](https://community.freefem.org/t/plot-in-3d-with-vtu-and-paraview/57 "2019-05-24T17:35:30Z")
Hi i have to plot the Following function: q(x/eps,y/eps,z/eps)=1 if (x/eps,y/eps,z/eps) \\in B\_{\\delta}+ Z^3, else 0. where B\_{delta} is the ball with radius \\delta= ((3/4)(1/(wpi)))^{1/3} we choise eps=0.1 and w=200… --- ## [Parabolic problem in 3D](https://community.freefem.org/t/parabolic-problem-in-3d/56)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [May 23, 2019, 4:56pm UTC](https://community.freefem.org/t/parabolic-problem-in-3d/56 "2019-05-23T16:56:29Z")
Hi, i write the Following code to calculate the solution of two problems du/dt-Delta u+ qdelta(x/eps,y/eps,z/eps) u/(1+u)= 0.25sin(2pi\*x), (x,y,z) \\in (0,1)^3, t \\in \[0,1) avec la condition initiale u(x,0)=0 et les co… --- ## [Code en dimension 3](https://community.freefem.org/t/code-en-dimension-3/55)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [May 22, 2019, 4:49pm UTC](https://community.freefem.org/t/code-en-dimension-3/55 "2019-05-22T16:49:18Z")
Bonjour j’ai le code suivant qui est en dimension deux d’espace. Quels changements faire pour qu’il soit en dimension 3 d’espace, c’est à dire (x,y,z) \\in (0,1)^3 et t \\in (0,1)? S’il vous plaît load "UMFPACK64" defau… --- ## [About the functions LinearCG](https://community.freefem.org/t/about-the-functions-linearcg/54)
**Author:** [@Charles](https://community.freefem.org/u/Charles)\ **Replies:** 7\ **Last updated:** [May 21, 2019, 1:38am UTC](https://community.freefem.org/t/about-the-functions-linearcg/54 "2019-05-21T01:38:19Z")
Hi everyone! Just a small question about the precise nomenclature of the function LinearCG. If I try to solve a very basic Poisson problem with homogeneous Dirichlet BC, the following piece of code works just fine: va… --- ## [Axisymmetric navier-Stokes](https://community.freefem.org/t/axisymmetric-navier-stokes/38)
**Author:** [@gerard](https://community.freefem.org/u/gerard)\ **Replies:** 1\ **Last updated:** [May 10, 2019, 7:00pm UTC](https://community.freefem.org/t/axisymmetric-navier-stokes/38 "2019-05-10T19:00:49Z")
i solve axisymmetric Navier-Stokes equation with periodic boundary condition in 2D domain. my first question : how can i do to represent the solution in the rest of the domain in 2D . Example suppose i solve the equ… --- ## [Calculer le max sur (x,y) d'une fonction (x,y,t)](https://community.freefem.org/t/calculer-le-max-sur-x-y-dune-fonction-x-y-t/48)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 5\ **Last updated:** [May 9, 2019, 8:35am UTC](https://community.freefem.org/t/calculer-le-max-sur-x-y-dune-fonction-x-y-t/48 "2019-05-09T08:35:15Z")
Bonjour j’ai le code suivant et je souhaite calculer eh(t)= max\_{x,y} |uh(x,y,t)-wh(x,y,t)| où uh et wh sont deux solutions de deux problèmes différents calculer dans le code. Le voici joint et je vous remercie par av… --- ## [Corner singularity on polar coordinates](https://community.freefem.org/t/corner-singularity-on-polar-coordinates/49)
**Author:** [@eliseo](https://community.freefem.org/u/eliseo)\ **Replies:** 0\ **Last updated:** [May 8, 2019, 10:47am UTC](https://community.freefem.org/t/corner-singularity-on-polar-coordinates/49 "2019-05-08T10:47:15Z")
Dear all, the first code below shows the standard and well-known singularity on the corner domain. My surprise is when solving the same problem using polar coordinates and the singularity on the origin seems to unfold… --- ## [GUI implementation](https://community.freefem.org/t/gui-implementation/40)
**Author:** [@nicola\_poli](https://community.freefem.org/u/nicola_poli)\ **Replies:** 2\ **Last updated:** [May 7, 2019, 1:00pm UTC](https://community.freefem.org/t/gui-implementation/40 "2019-05-07T13:00:18Z")
Hi everyone, I am working with a student to implement a GUI, starting from one of my code in FreeFem++. Do you have any experience with a similar task? I know about Freefem-cs, so I suppose that a GUI in Freefem is poss… --- ## [An issue for h-adaptation in FreeFem++](https://community.freefem.org/t/an-issue-for-h-adaptation-in-freefem/33)
**Author:** [@zhaog6](https://community.freefem.org/u/zhaog6)\ **Replies:** 0\ **Last updated:** [April 25, 2019, 3:12pm UTC](https://community.freefem.org/t/an-issue-for-h-adaptation-in-freefem/33 "2019-04-25T15:12:04Z")
Hello, I’d like to implement h-adaptation on structured grids. I find the mesh quality doesn’t seem to be good when using splitmesh to refine mesh locally, because splitmesh(...) is not based on the partition principle … --- ## [Computing 3D integral with mixed/vector element variables is very slow](https://community.freefem.org/t/computing-3d-integral-with-mixed-vector-element-variables-is-very-slow/30)
**Author:** [@ffeppon](https://community.freefem.org/u/ffeppon)\ **Replies:** 0\ **Last updated:** [April 20, 2019, 11:49am UTC](https://community.freefem.org/t/computing-3d-integral-with-mixed-vector-element-variables-is-very-slow/30 "2019-04-20T11:49:22Z")
Hello, I noticed that the computation of 3D integrals with \[P1,P1,P1\] elements is about ten times slower compared to the integration with P1 elements (after interpolating each coordinate), see the code below and the fil… --- ## [Index of etak and Triangles](https://community.freefem.org/t/index-of-etak-and-triangles/25)
**Author:** [@wys](https://community.freefem.org/u/wys)\ **Replies:** 1\ **Last updated:** [April 16, 2019, 7:58am UTC](https://community.freefem.org/t/index-of-etak-and-triangles/25 "2019-04-16T07:58:03Z")
Dear all, Another simple question arises when I run the AdaptResidualErrorIndicator.edp. I want to know the etak\[i\] corresponds to which element. I think maybe for example eatk\[0\] corresponds to the first triangle intr… --- ## [How to get the sub-matrix of A?](https://community.freefem.org/t/how-to-get-the-sub-matrix-of-a/23)
**Author:** [@wys](https://community.freefem.org/u/wys)\ **Replies:** 3\ **Last updated:** [April 13, 2019, 11:29am UTC](https://community.freefem.org/t/how-to-get-the-sub-matrix-of-a/23 "2019-04-13T11:29:34Z")
Dear all, I am new to FreeFEM++ and I want to ask a simple question. If I have already obtained a matrix by matrix A = va(Vh, Vh);, how to get the sub-matrix of A? For example in Matlab, you can simply write A(1:i, 1:… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=74) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=76)