# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=62 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 63 --- ## [Fix the value at a point](https://community.freefem.org/t/fix-the-value-at-a-point/882)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 5\ **Last updated:** [April 4, 2021, 8:37pm UTC](https://community.freefem.org/t/fix-the-value-at-a-point/882 "2021-04-04T20:37:22Z")
Dear all, How can I prescribe a value at a fixed point in FreeFEM++? For example, fix the velocity to be zero at the centre of a rotating disc; or fix the pressure at the reference point for a flow problem? Thanks in a… --- ## [Access matrix element](https://community.freefem.org/t/access-matrix-element/885)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 6\ **Last updated:** [April 4, 2021, 8:36pm UTC](https://community.freefem.org/t/access-matrix-element/885 "2021-04-04T20:36:53Z")
Dear all, I can understand we can create the system matrix in FreeFEM++, my question is: Can we modify the element of the matrix, such as putting a penalty (a large number) on the diagonal for a specific degree of free… --- ## [Prescribe a value for a fixed point](https://community.freefem.org/t/prescribe-a-value-for-a-fixed-point/884)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [March 31, 2021, 6:47pm UTC](https://community.freefem.org/t/prescribe-a-value-for-a-fixed-point/884 "2021-03-31T18:47:01Z")
Is there a method to do this in FreeFEM++? For example, fix the velocity at the centre of a disc so that it can keep rotating stably, or give a pressure reference point for a flow problem. Some one suggested do u\[\]\[n\]=… --- ## [Saving data inside a loop](https://community.freefem.org/t/saving-data-inside-a-loop/561)
**Author:** [@mordechaiy](https://community.freefem.org/u/mordechaiy)\ **Replies:** 1\ **Last updated:** [March 31, 2021, 2:44pm UTC](https://community.freefem.org/t/saving-data-inside-a-loop/561 "2021-03-31T14:44:23Z")
Hello, I have written in FreeFem++ a central differences scheme to the weak formulation of the 2D wave equation in a square. and initialized it with two initial conditions, then I have a loop for the time of the simula… --- ## [Movemesh does not work properly](https://community.freefem.org/t/movemesh-does-not-work-properly/883)
**Author:** [@sgkkr](https://community.freefem.org/u/sgkkr)\ **Replies:** 0\ **Last updated:** [March 31, 2021, 11:27am UTC](https://community.freefem.org/t/movemesh-does-not-work-properly/883 "2021-03-31T11:27:36Z")
I built discrete analytical expressions for transforming a rectangular mesh into a bump shape. I derived the expressions using spline curves on python and I am trying to use the same in FreeFem++ but it does not give me … --- ## [Partitioning the stiffness matrix without partitioning the mesh for PETSc](https://community.freefem.org/t/partitioning-the-stiffness-matrix-without-partitioning-the-mesh-for-petsc/875)
**Author:** [@Jeet](https://community.freefem.org/u/Jeet)\ **Replies:** 10\ **Last updated:** [March 27, 2021, 10:45am UTC](https://community.freefem.org/t/partitioning-the-stiffness-matrix-without-partitioning-the-mesh-for-petsc/875 "2021-03-27T10:45:54Z")
Hi FreeFEM developers! I thank you for having integrated PETSc with FreeFEM! This has resulted in an easy implementation of large scale topology optimization. I am attempting to implement a contact mechanics solver in… --- ## [Array definition](https://community.freefem.org/t/array-definition/874)
**Author:** [@zese](https://community.freefem.org/u/zese)\ **Replies:** 1\ **Last updated:** [March 26, 2021, 6:05pm UTC](https://community.freefem.org/t/array-definition/874 "2021-03-26T18:05:48Z")
Dear all, I want to define an array which I don’t know about its size at the first place and it is updated every iteration in a for loop. how I can define it? Best regards --- ## [Cyclic boundary conditions](https://community.freefem.org/t/cyclic-boundary-conditions/873)
**Author:** [@marcodeba](https://community.freefem.org/u/marcodeba)\ **Replies:** 0\ **Last updated:** [March 26, 2021, 11:07am UTC](https://community.freefem.org/t/cyclic-boundary-conditions/873 "2021-03-26T11:07:58Z")
Goodmorning everybody, I’m using freefem for the solution of magnetostatic problems. My problem is the simulation of a toroidal solenoid that of course it is discrete over the toroidal direction since it is composed, ov… --- ## [Identify regions in a mesh imported from Gmsh](https://community.freefem.org/t/identify-regions-in-a-mesh-imported-from-gmsh/867)
**Author:** [@marcodeba](https://community.freefem.org/u/marcodeba)\ **Replies:** 6\ **Last updated:** [March 26, 2021, 9:20am UTC](https://community.freefem.org/t/identify-regions-in-a-mesh-imported-from-gmsh/867 "2021-03-26T09:20:11Z")
Hi everybody! I’m having some troubles in the identifications of different regions into a mesh imported from Gmsh with the format .mesh with the line: mesh3 Th = readmesh3(“Trial1.mesh”); The loading of the mesh is pe… --- ## [Integral formula](https://community.freefem.org/t/integral-formula/864)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 1\ **Last updated:** [March 20, 2021, 2:31pm UTC](https://community.freefem.org/t/integral-formula/864 "2021-03-20T14:31:36Z")
Hi, please hows we write in FF++, the formula: \\int\_{t-\\tau-h}^{t-\\tau+h} I(x,s) ds ? where h is an integer avec I(x,s) is function solution of an other problem Regards --- ## [vtkloadS("mymesh.vtk")](https://community.freefem.org/t/vtkloads-mymesh-vtk/868)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 1\ **Last updated:** [March 25, 2021, 8:04pm UTC](https://community.freefem.org/t/vtkloads-mymesh-vtk/868 "2021-03-25T20:04:23Z")
Dear FreeFEM users, I have tried several formats of “mymesh.vtk” using the following code, and all failed load “iovtk” meshS ThS=vtkloadS(“mymesh.vtk”); Can someone please provide a simple example of “mymesh.vtk”? T… --- ## [Nodes in boundary](https://community.freefem.org/t/nodes-in-boundary/869)
**Author:** [@Daoudi](https://community.freefem.org/u/Daoudi)\ **Replies:** 1\ **Last updated:** [March 25, 2021, 7:52pm UTC](https://community.freefem.org/t/nodes-in-boundary/869 "2021-03-25T19:52:33Z")
Hi, how can I find the indixs of nodes in the boundary of mesh in (2d) --- ## [Thermal Bridge heat Transfer](https://community.freefem.org/t/thermal-bridge-heat-transfer/871)
**Author:** [@arete](https://community.freefem.org/u/arete)\ **Replies:** 1\ **Last updated:** [March 25, 2021, 7:19pm UTC](https://community.freefem.org/t/thermal-bridge-heat-transfer/871 "2021-03-25T19:19:36Z")
Hi i try to solve thermal bridge example of Featool https://www.featool.com/doc/heat\_transfer\_05\_thermal\_bridge1#tut\_ht05 my heat equation with convection and diffusion problem heat(u,v) = int2d(Th)( kappa \* (dx(u) \*… --- ## [Use meshL to define an interval](https://community.freefem.org/t/use-meshl-to-define-an-interval/866)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 3\ **Last updated:** [March 24, 2021, 2:27pm UTC](https://community.freefem.org/t/use-meshl-to-define-an-interval/866 "2021-03-24T14:27:35Z")
Hi, please how we can youse meshL to define an interval \[a,b\]? Using segment. I don’t find examples. Regards --- ## [Use of restriction on a meshL and matrix free operator](https://community.freefem.org/t/use-of-restriction-on-a-meshl-and-matrix-free-operator/862)
**Author:** [@LucasPa](https://community.freefem.org/u/LucasPa)\ **Replies:** 5\ **Last updated:** [March 23, 2021, 2:01pm UTC](https://community.freefem.org/t/use-of-restriction-on-a-meshl-and-matrix-free-operator/862 "2021-03-23T14:01:17Z")
Hi, I would like to define a square matrix-free operator which dimension corresponds to the size of the restricted space that corresponds to the left boundary of the 2d domain. So basically the operator behaves as: ano… --- ## [Construct 3D mesh from surface triangles](https://community.freefem.org/t/construct-3d-mesh-from-surface-triangles/865)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [March 23, 2021, 12:05pm UTC](https://community.freefem.org/t/construct-3d-mesh-from-surface-triangles/865 "2021-03-23T12:05:01Z")
Hi, I have some surface triangular meshes in VTK format. Is there a quick way to construct the volumetric mesh based upon these surface triangles? Thanks in advance. Yongxing. --- ## [Utilising ffddm](https://community.freefem.org/t/utilising-ffddm/861)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 4\ **Last updated:** [March 18, 2021, 4:57pm UTC](https://community.freefem.org/t/utilising-ffddm/861 "2021-03-18T16:57:58Z")
Hello developers, When I want to use ffddm I get an error " The identifier mpsize doesn’t exist. For using ffddm I have to install a package or add particular library? I just tried a simple command, but got error. ff… --- ## [Diffusion coefficient between two PDEs](https://community.freefem.org/t/diffusion-coefficient-between-two-pdes/858)
**Author:** [@nmmhuynh](https://community.freefem.org/u/nmmhuynh)\ **Replies:** 8\ **Last updated:** [March 18, 2021, 1:10pm UTC](https://community.freefem.org/t/diffusion-coefficient-between-two-pdes/858 "2021-03-18T13:10:34Z")
Hi everyone! I am sequentially solving two PDEs, correlated by the diffusion term: After solving the first PDE (thus getting u) with solve firstpde (u, v) = int3d (Th) ( A \* grad(u)’ \* grad(v) ) + BCs ) ; where T… --- ## [Mixed Boundary Condition and Periodic System](https://community.freefem.org/t/mixed-boundary-condition-and-periodic-system/860)
**Author:** [@kevinmo08](https://community.freefem.org/u/kevinmo08)\ **Replies:** 0\ **Last updated:** [March 17, 2021, 9:44pm UTC](https://community.freefem.org/t/mixed-boundary-condition-and-periodic-system/860 "2021-03-17T21:44:49Z")
Hi all, I am interested in solving the Laplace equation in 2D with periodic boundary conditions and a mixed boundary condition on an inner circle. The mixed boundary condition is $$ n \\cdot \\grad u = cos(x) $$ Where … --- ## [Moving a bead in a viscoelastic medium 3D](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847)
**Author:** [@Srj](https://community.freefem.org/u/Srj)\ **Replies:** 5\ **Last updated:** [March 17, 2021, 4:26pm UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847 "2021-03-17T16:26:26Z")
I would like to model a (spherical) bead in a (spherical) 3D visco-elastic medium. The bead is first moved around actively by external forces. Once these forces stop, I want to find out the movement of the bead due to … --- ## [Extract of left and right vectors of multidimensional SVD](https://community.freefem.org/t/extract-of-left-and-right-vectors-of-multidimensional-svd/844)
**Author:** [@LucasPa](https://community.freefem.org/u/LucasPa)\ **Replies:** 19\ **Last updated:** [March 17, 2021, 8:53am UTC](https://community.freefem.org/t/extract-of-left-and-right-vectors-of-multidimensional-svd/844 "2021-03-17T08:53:16Z")
Hi, I try to adapt the example “mf-2d-SLEPc.edp” to compute singular values for a multi-dimensional problem. Namely, I want to compute the singular values of the operator MF Mat\ MF(Qu, Qf, prodFunc, transpose… --- ## [Export PETSc Mat to python](https://community.freefem.org/t/export-petsc-mat-to-python/845)
**Author:** [@koenstrien](https://community.freefem.org/u/koenstrien)\ **Replies:** 8\ **Last updated:** [March 16, 2021, 7:50am UTC](https://community.freefem.org/t/export-petsc-mat-to-python/845 "2021-03-16T07:50:08Z")
Hi There, I am trying to export a PETSc Mat type to python to continue working on it there. I save the Mat type using load "PETSc" Mat A; ... // Filling A ObjectView(A, format = "binary", name = "A.dat"); Afterward… --- ## [Reading mesh MPI](https://community.freefem.org/t/reading-mesh-mpi/854)
**Author:** [@Robert](https://community.freefem.org/u/Robert)\ **Replies:** 8\ **Last updated:** [March 14, 2021, 10:01pm UTC](https://community.freefem.org/t/reading-mesh-mpi/854 "2021-03-14T22:01:20Z")
Dear forum, I am running FreeFEM++ 4.8 version on Windows 10. I am trying to run the program in parallel. I started to study the examples available but it seems I have an error when it comes to reading existing mesh fil… --- ## [Report on memory and storage use](https://community.freefem.org/t/report-on-memory-and-storage-use/851)
**Author:** [@hamed](https://community.freefem.org/u/hamed)\ **Replies:** 3\ **Last updated:** [March 14, 2021, 5:48pm UTC](https://community.freefem.org/t/report-on-memory-and-storage-use/851 "2021-03-14T17:48:59Z")
Is there anyway to get a report on the amound of RAM and storage used during the computation? I can easily find the computational time at the end of .log file. I was wondering if there is any further information? time… --- ## [3D error and warning](https://community.freefem.org/t/3d-error-and-warning/850)
**Author:** [@guanzhen](https://community.freefem.org/u/guanzhen)\ **Replies:** 1\ **Last updated:** [March 13, 2021, 5:45pm UTC](https://community.freefem.org/t/3d-error-and-warning/850 "2021-03-13T17:45:03Z")
Dear Sir/Madam When I solve a 3D example with FreeFEM, the following error has occurred: “Error umpfack umfpack\_di\_numeric status -1 Error umfpack\_di\_solve status -3” I don’t know why? Thank you very much! --- ## [Minimize cost function with BFGS algorithm FreeFem?](https://community.freefem.org/t/minimize-cost-function-with-bfgs-algorithm-freefem/843)
**Author:** [@Lemin](https://community.freefem.org/u/Lemin)\ **Replies:** 4\ **Last updated:** [March 9, 2021, 2:36pm UTC](https://community.freefem.org/t/minimize-cost-function-with-bfgs-algorithm-freefem/843 "2021-03-09T14:36:59Z")
Hello, I have a cost function and its gradient calculated with finite element discretization (values at integrations points) and I have the data in a text file. How to minimize this function? any idea? Thanks for you… --- ## [\[SOLVED\] Prolongation/restriction matrix](https://community.freefem.org/t/solved-prolongation-restriction-matrix/841)
**Author:** [@LucasPa](https://community.freefem.org/u/LucasPa)\ **Replies:** 2\ **Last updated:** [March 8, 2021, 3:38pm UTC](https://community.freefem.org/t/solved-prolongation-restriction-matrix/841 "2021-03-08T15:38:16Z")
Hi everyone ! I am solving Navier-Stokes equations, on a \[P2, P2, P1\] space (velocity-velocity-pressure): func PuPuPp=\[P2, P2, P1\]; fespace Uvvp(Th, PuPuPp); Uvvp \[ux,uy,up\]; Moreover I define a space just for the… --- ## [Usage of PETSc's 'Mat' type](https://community.freefem.org/t/usage-of-petscs-mat-type/835)
**Author:** [@koenstrien](https://community.freefem.org/u/koenstrien)\ **Replies:** 2\ **Last updated:** [March 8, 2021, 3:28pm UTC](https://community.freefem.org/t/usage-of-petscs-mat-type/835 "2021-03-08T15:28:54Z")
Hi all, I am new to FreeFEM and I am figuring out how to use FreeFEM with the PETSc interface. Now I am learning about the Mat type of the PETSc package, but I do not fully understand all the functions that come with it… --- ## [Problem on convergence rate for Reynolds no=10 or above 10, for time dependent Navier-Stokes equations](https://community.freefem.org/t/problem-on-convergence-rate-for-reynolds-no-10-or-above-10-for-time-dependent-navier-stokes-equations/836)
**Author:** [@bikram](https://community.freefem.org/u/bikram)\ **Replies:** 0\ **Last updated:** [March 5, 2021, 2:07pm UTC](https://community.freefem.org/t/problem-on-convergence-rate-for-reynolds-no-10-or-above-10-for-time-dependent-navier-stokes-equations/836 "2021-03-05T14:07:23Z")
Dear all, I am trying to compute the L2 velocity rate for time dependent Navier-Stokes equations using P2-P1 finite element space. when I take Reynolds number =1, then it works well, but when I take Reynolds number= 10 … --- ## [Migration to FreeFEM](https://community.freefem.org/t/migration-to-freefem/834)
**Author:** [@Dave](https://community.freefem.org/u/Dave)\ **Replies:** 0\ **Last updated:** [March 5, 2021, 1:02am UTC](https://community.freefem.org/t/migration-to-freefem/834 "2021-03-05T01:02:32Z")
I want to migrate my FEM code from one of the big, commercial FEM tools (Abaqus) to FreeFEM. Is there any documentation or support, or does anyone have experience in doing this? [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=61) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=63)