# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=69 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 70 --- ## [Function "dscalprod"](https://community.freefem.org/t/function-dscalprod/509)
**Author:** [@julienG](https://community.freefem.org/u/julienG)\ **Replies:** 2\ **Last updated:** [July 20, 2020, 8:51pm UTC](https://community.freefem.org/t/function-dscalprod/509 "2020-07-20T20:51:07Z")
Hi all, After a while without updating FreeFem (around 3.62), I am trying to now trying to update my codes. In earlier version I was using the function dscalprod which seems not to exist anymore. I guess the syntax sl… --- ## [Solving Poisson Equation on 1D mesh with Dirichlet BC](https://community.freefem.org/t/solving-poisson-equation-on-1d-mesh-with-dirichlet-bc/507)
**Author:** [@balance](https://community.freefem.org/u/balance)\ **Replies:** 1\ **Last updated:** [July 15, 2020, 5:48pm UTC](https://community.freefem.org/t/solving-poisson-equation-on-1d-mesh-with-dirichlet-bc/507 "2020-07-15T17:48:21Z")
Hello, so assume you want to solve: int\_0^1 grad(u)grad(v) dx = int\_0^1 v dx on \[0,1\] mesh with let’s say N=5 cells (i.e. 6 nodes). For the basis, we want to use tent functions. I.e. something like this Tent functions … --- ## [Ellipse with FF+](https://community.freefem.org/t/ellipse-with-ff/506)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 4\ **Last updated:** [July 14, 2020, 9:56am UTC](https://community.freefem.org/t/ellipse-with-ff/506 "2020-07-14T09:56:02Z")
Hi, how we can define an ellipse with FF++ and plot it? Regards --- ## [Creating Mat\ from Mat\](https://community.freefem.org/t/creating-mat-complex-from-mat-real/502)
**Author:** [@cmd](https://community.freefem.org/u/cmd)\ **Replies:** 12\ **Last updated:** [July 13, 2020, 12:48pm UTC](https://community.freefem.org/t/creating-mat-complex-from-mat-real/502 "2020-07-13T12:48:24Z")
Hopefully this is an easy question! I have a problem involving both real and complex arithmetic. Once I have done: Mat\ Areal; Mat\ Acplx; buildDmesh(Th); createMat(Th,Areal,Pk); How can I then apply the … --- ## [Using "-cd" option of command line](https://community.freefem.org/t/using-cd-option-of-command-line/483)
**Author:** [@arousta](https://community.freefem.org/u/arousta)\ **Replies:** 3\ **Last updated:** [July 11, 2020, 1:23pm UTC](https://community.freefem.org/t/using-cd-option-of-command-line/483 "2020-07-11T13:23:00Z")
I see there is a “-cd” option which FreeFem++ command takes. I think it means that FreeFem first cd into that directory and then runs. But I couldn’t figure out how to use it. E.g. I have these files in /home/ar/code: … --- ## [Unable to display the plot value for velocity](https://community.freefem.org/t/unable-to-display-the-plot-value-for-velocity/503)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 9\ **Last updated:** [July 11, 2020, 3:20am UTC](https://community.freefem.org/t/unable-to-display-the-plot-value-for-velocity/503 "2020-07-11T03:20:22Z")
Hello Everyone, I am not getting the plot for \[u1, u2\]. kindly, suggest me to fix it. code has been given as: /\* coupled equation is u\_x + v\_y = 0 ((u,v).grad(u,v))\* + grad(p) -1/Re \* ( lap(u, v) ) = 0 (u, v). ( grad… --- ## [Recover correspondence between 2d mesh and sufrace mesh](https://community.freefem.org/t/recover-correspondence-between-2d-mesh-and-sufrace-mesh/496)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 5\ **Last updated:** [July 10, 2020, 3:01pm UTC](https://community.freefem.org/t/recover-correspondence-between-2d-mesh-and-sufrace-mesh/496 "2020-07-10T15:01:44Z")
Hello, as seen in the FreeFEM documentation, it is possible to construct surface meshes starting from two dimensional meshes using the command movemesh23. When doing this (for example in the case of a sphere) some point… --- ## [Acoustic Equation and its program](https://community.freefem.org/t/acoustic-equation-and-its-program/492)
**Author:** [@AKS](https://community.freefem.org/u/AKS)\ **Replies:** 6\ **Last updated:** [July 7, 2020, 4:28pm UTC](https://community.freefem.org/t/acoustic-equation-and-its-program/492 "2020-07-07T16:28:20Z")
Hello, I am somewhat new to FreeFEM. Using it for acoustic analysis. Can someone please help me in knowing how the example code is working. I’m unable to get: How the direction of flow is defined (it is given in docume… --- ## [Non-Dimensional Equation error](https://community.freefem.org/t/non-dimensional-equation-error/489)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 0\ **Last updated:** [July 4, 2020, 5:42pm UTC](https://community.freefem.org/t/non-dimensional-equation-error/489 "2020-07-04T17:42:47Z")
Dear @frederichecht, @prj Sir, I am trying to formulate the non-linear equation based on your suggestions and link provide before. topic name relevant problem by prj relevant problem by frederichecht I am trying to… --- ## [Trunc assertion fail ie==nbe](https://community.freefem.org/t/trunc-assertion-fail-ie-nbe/487)
**Author:** [@Jonas\_Zille](https://community.freefem.org/u/Jonas_Zille)\ **Replies:** 3\ **Last updated:** [July 2, 2020, 2:16pm UTC](https://community.freefem.org/t/trunc-assertion-fail-ie-nbe/487 "2020-07-02T14:16:53Z")
Hi guys, once more I have a question regarding meshing in FreeFEM. My goal is to build a hourglass-esque mesh with equidistant layering in z (this is later important to impose the BCs). Layer-by-layer I want to add th… --- ## [Dispatching RT0 components from sol](https://community.freefem.org/t/dispatching-rt0-components-from-sol/485)
**Author:** [@hamed](https://community.freefem.org/u/hamed)\ **Replies:** 8\ **Last updated:** [June 30, 2020, 11:37am UTC](https://community.freefem.org/t/dispatching-rt0-components-from-sol/485 "2020-06-30T11:37:39Z")
I have a solution obtained by variational form of RT0 fespace fespace Eh(Th,RT0Ortho); Eh\ \[Ax,Ay\]; varf vK11(\[ux,uy\],\[vx,vy\]) =int2d(Th)( nu \* (dx(vy)-dy(vx)) \* (dx(uy)-dy(ux)) … --- ## [MUMPS, solve and possible memory leaks](https://community.freefem.org/t/mumps-solve-and-possible-memory-leaks/168)
**Author:** [@Alexander1](https://community.freefem.org/u/Alexander1)\ **Replies:** 2\ **Last updated:** [June 29, 2020, 9:11am UTC](https://community.freefem.org/t/mumps-solve-and-possible-memory-leaks/168 "2020-06-29T09:11:17Z")
Dear all, I am trying to parallelize a solution of a nonlinear time-dependent problem using FreeFEM++ 4.2.1 with the MUMPS package. At every time step I use “solve” in this way load “MUMPS” … for (int m = 0; m\ **Author:** [@arousta](https://community.freefem.org/u/arousta)\ **Replies:** 0\ **Last updated:** [June 27, 2020, 3:24pm UTC](https://community.freefem.org/t/buildmesh-option-similar-to-splitpbedge/484 "2020-06-27T15:24:54Z") Does buildmesh function have an option like splitpbedge of adaptmesh function? If not it would be useful to have … --- ## [Is the way borders are listed in the buildmesh argument critical?](https://community.freefem.org/t/is-the-way-borders-are-listed-in-the-buildmesh-argument-critical/482)
**Author:** [@denis.crete](https://community.freefem.org/u/denis.crete)\ **Replies:** 0\ **Last updated:** [June 22, 2020, 1:52pm UTC](https://community.freefem.org/t/is-the-way-borders-are-listed-in-the-buildmesh-argument-critical/482 "2020-06-22T13:52:50Z")
Hello, I observed, with the attached code, a dependence of the results on the line starting with “mesh th=buildmesh(…”. Case 1: mesh th=buildmesh(rig(m)+lef(m)+bot(20\*m)+top(20\*m)); does not give the same results as … --- ## [Variational formulation](https://community.freefem.org/t/variational-formulation/481)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [June 21, 2020, 9:23am UTC](https://community.freefem.org/t/variational-formulation/481 "2020-06-21T09:23:08Z")
Hi i have a question please. We consider the following equation: L\*(du/dt - \\Delta u + c(x,y) . \\nabla u + w q\_{\\delta}(x/\\eps,y/eps) u) = L\*f(x,t), x \\in \[0,1\], t \\in \[0,1\], where L is real fixed and esp is positif … --- ## [Resize to bigger dimension removes non-zero coefficients in sparse matrix?](https://community.freefem.org/t/resize-to-bigger-dimension-removes-non-zero-coefficients-in-sparse-matrix/477)
**Author:** [@Colin](https://community.freefem.org/u/Colin)\ **Replies:** 2\ **Last updated:** [June 19, 2020, 2:33pm UTC](https://community.freefem.org/t/resize-to-bigger-dimension-removes-non-zero-coefficients-in-sparse-matrix/477 "2020-06-19T14:33:01Z")
Hello, I am trying to resize a sparse matrix, but it appears to eliminate non-zeros coefficients? See below code and output. Many thanks for the help! Regards, Colin Code: int nnz=44330306; int\[int\] I(nnz),J(nnz); … --- ## [Overlapping mesh - integral calculation](https://community.freefem.org/t/overlapping-mesh-integral-calculation/458)
**Author:** [@aszaboa](https://community.freefem.org/u/aszaboa)\ **Replies:** 11\ **Last updated:** [June 19, 2020, 12:41pm UTC](https://community.freefem.org/t/overlapping-mesh-integral-calculation/458 "2020-06-19T12:41:35Z")
Dear FreeFem++ Users! I am trying to solve the linearized Navier-Stokes equation using and overlapping mesh, based on the available codes. Although I am managing getting things done, there are a few things I do not unde… --- ## [Application of Dirichlet BCs](https://community.freefem.org/t/application-of-dirichlet-bcs/467)
**Author:** [@chenna](https://community.freefem.org/u/chenna)\ **Replies:** 6\ **Last updated:** [June 17, 2020, 3:35pm UTC](https://community.freefem.org/t/application-of-dirichlet-bcs/467 "2020-06-17T15:35:38Z")
Hello FreeFem community, I started using FreeFEM. I find it very easy to understand and use. I started liking it and considering to integrate it into my research workflow. I am looking for some clarification regarding t… --- ## [Get labels of boundary nodes for P2 elements](https://community.freefem.org/t/get-labels-of-boundary-nodes-for-p2-elements/471)
**Author:** [@Julien](https://community.freefem.org/u/Julien)\ **Replies:** 7\ **Last updated:** [June 16, 2020, 11:28am UTC](https://community.freefem.org/t/get-labels-of-boundary-nodes-for-p2-elements/471 "2020-06-16T11:28:03Z")
Hi everyone! I use FreeFem++ to get the matrices of a given problem and then solve the system in Matlab for some reason. I build the matrices with P2 elements. However I need to export the label (for boundary elements) … --- ## [Plot an function](https://community.freefem.org/t/plot-an-function/474)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [June 16, 2020, 9:59am UTC](https://community.freefem.org/t/plot-an-function/474 "2020-06-16T09:59:03Z")
Hi, i want to plot with FF++ the graph of the function u(t,x) defined by u(t,x)= -2\*\\nu\* \\alpha(t)+b(t)\*x +c(t), \\ t \\in \[0,1\], x \\in \[0,1\] where \\nu=0.01 and b'(t)=-b^2(t)+f(t), \\alpha(t)= \\exp(-\\int b(t) dt), … --- ## [Définition d'une fonction](https://community.freefem.org/t/definition-dune-fonction/470)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [June 15, 2020, 8:45am UTC](https://community.freefem.org/t/definition-dune-fonction/470 "2020-06-15T08:45:17Z")
J’ai la fonction suivante : q\_{\\delta}(x/eps,y/eps)= 1 si (x/eps,y/eps) \\in B\_{\\delta} x Z^2, et 0 sinon. \\eps est fixé, B\_{\\delta}= {x : |x| \< \\delta} tel que \\delta = \\sqrt{1/(\\pi\*w)}, et w est fixé. Je sais program… --- ## [Error operator \* product of matrices](https://community.freefem.org/t/error-operator-product-of-matrices/469)
**Author:** [@Mathieu.S](https://community.freefem.org/u/Mathieu.S)\ **Replies:** 2\ **Last updated:** [June 15, 2020, 4:24pm UTC](https://community.freefem.org/t/error-operator-product-of-matrices/469 "2020-06-15T16:24:47Z")
Hello, I am currently working with FreeFrem during my internship and I get an error which I don’t understand. You can find my code following the link bellow my message. I took the code (which works) already written in t… --- ## [Interfacing between FreeFEM and FEniCS/Dolfin](https://community.freefem.org/t/interfacing-between-freefem-and-fenics-dolfin/463)
**Author:** [@lutz.lesshafft](https://community.freefem.org/u/lutz.lesshafft)\ **Replies:** 3\ **Last updated:** [June 15, 2020, 2:48pm UTC](https://community.freefem.org/t/interfacing-between-freefem-and-fenics-dolfin/463 "2020-06-15T14:48:24Z")
Dear FreeFEM gurus, for debugging purposes, I want to export a 2D flow field (base flow for linear stability analysis) from FF++ to FEniCS, together with the mesh. The mesh is created from an edp file, the flow field c… --- ## [How to get the data from the P2](https://community.freefem.org/t/how-to-get-the-data-from-the-p2/296)
**Author:** [@Dylan](https://community.freefem.org/u/Dylan)\ **Replies:** 3\ **Last updated:** [June 12, 2020, 12:52pm UTC](https://community.freefem.org/t/how-to-get-the-data-from-the-p2/296 "2020-06-12T12:52:14Z")
Dear all, I use the P2 and P1 to compare with analytical solution by paraview. The error of P2 is bigger than P1. I know that the warning " Finite element variables saved using paraview must be in P0 or P1 ". Why no… --- ## [Partial periodic boundary condition erroe](https://community.freefem.org/t/partial-periodic-boundary-condition-erroe/465)
**Author:** [@wangicewing](https://community.freefem.org/u/wangicewing)\ **Replies:** 1\ **Last updated:** [June 11, 2020, 8:58am UTC](https://community.freefem.org/t/partial-periodic-boundary-condition-erroe/465 "2020-06-11T08:58:39Z")
Square mesh : nb vertices =3321 , nb triangles = 6400 , nb boundary edges 240 Problem build of FEspace (2d) (may be : due to periodic Boundary condition missing ) FH The number of DF must be 55120 and it is 55485 … --- ## [Solve PDE with infinite nb of solutions by adding a constraint](https://community.freefem.org/t/solve-pde-with-infinite-nb-of-solutions-by-adding-a-constraint/462)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 2\ **Last updated:** [June 11, 2020, 7:54am UTC](https://community.freefem.org/t/solve-pde-with-infinite-nb-of-solutions-by-adding-a-constraint/462 "2020-06-11T07:54:39Z")
Hello, I would like to use FreeFEM to solve a PDE with an infinte number of solutions, and recover a unique solution by imposing a constraint. I found some other post on the forum linking to this page: http://jolivet.p… --- ## [How to assemble restriction matrix to extract the DoFs on the boundary](https://community.freefem.org/t/how-to-assemble-restriction-matrix-to-extract-the-dofs-on-the-boundary/460)
**Author:** [@Psywah](https://community.freefem.org/u/Psywah)\ **Replies:** 2\ **Last updated:** [June 10, 2020, 10:18am UTC](https://community.freefem.org/t/how-to-assemble-restriction-matrix-to-extract-the-dofs-on-the-boundary/460 "2020-06-10T10:18:18Z")
Hi, I want to assemble a restriction matrix to extract the DoFs on part of the boundary. I know the interpolate function can assemble such matrix by providing two FE function spaces. Can we define a P1 function space … --- ## [Computing eigenvalues](https://community.freefem.org/t/computing-eigenvalues/452)
**Author:** [@e-aranda](https://community.freefem.org/u/e-aranda)\ **Replies:** 4\ **Last updated:** [June 10, 2020, 9:49am UTC](https://community.freefem.org/t/computing-eigenvalues/452 "2020-06-10T09:49:23Z")
Hello, could anybody explain me why arpack is not able to compute the eigenvalues in this example? matrix C = \[\[ 2, -1, -1, 0\], \[-1, 1, 0, 0\], \[-1, 0, 2, -1\], \[ 0, 0, -1, 1\]\]; set(C,solver=UMFPACK); func r… --- ## [Extract Iso Surface in 3D](https://community.freefem.org/t/extract-iso-surface-in-3d/36)
**Author:** [@Jonas\_Zille](https://community.freefem.org/u/Jonas_Zille)\ **Replies:** 5\ **Last updated:** [June 10, 2020, 9:46am UTC](https://community.freefem.org/t/extract-iso-surface-in-3d/36 "2020-06-10T09:46:36Z")
Hi everyone, I recently installed FreeFem because I am interested in the 3d mesh adaption routines (very satisified with that so far). My problem right now is, that I want to solve a 3 dimensional PDE (with a scalar so… --- ## [Find Iso surface to impose BC](https://community.freefem.org/t/find-iso-surface-to-impose-bc/83)
**Author:** [@Jonas\_Zille](https://community.freefem.org/u/Jonas_Zille)\ **Replies:** 3\ **Last updated:** [June 10, 2020, 9:45am UTC](https://community.freefem.org/t/find-iso-surface-to-impose-bc/83 "2020-06-10T09:45:04Z")
Hi fellow FreeFEM’er, I have a 3D mesh on which I solve a PDE (time=i), for the solution in the next timestep i+1, I need to impose additional boundary conditions on the iso surface through the 3d volume (time: i). How… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=68) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=70)