# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=61 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 62 --- ## [How to access normal vectors of each discretised tetrahedron element](https://community.freefem.org/t/how-to-access-normal-vectors-of-each-discretised-tetrahedron-element/948)
**Author:** [@Daokun](https://community.freefem.org/u/Daokun)\ **Replies:** 0\ **Last updated:** [April 26, 2021, 4:11pm UTC](https://community.freefem.org/t/how-to-access-normal-vectors-of-each-discretised-tetrahedron-element/948 "2021-04-26T16:11:18Z")
Dear all, I am trying to apply a variable compressive body force to a 3D cantilever model. The compressive force has no certain direction in a global scale.So I am trying to apply this compressive force on faces of each… --- ## [X+a\*Y with PETSc matrix (Mat)](https://community.freefem.org/t/x-a-y-with-petsc-matrix-mat/940)
**Author:** [@Pmollo](https://community.freefem.org/u/Pmollo)\ **Replies:** 2\ **Last updated:** [April 26, 2021, 7:20am UTC](https://community.freefem.org/t/x-a-y-with-petsc-matrix-mat/940 "2021-04-26T07:20:15Z")
Hi, As said in the title, I am trying to compute X=X+a\*Y where X and Y are Mat PETSc matrices and a is a scalar. Is there a way to do this ? Here a stupid example : load "PETSc" mesh Th = square(10,10); fespace Vh(Th,P… --- ## [Adaptive algorithm using blue-green marking strategy](https://community.freefem.org/t/adaptive-algorithm-using-blue-green-marking-strategy/943)
**Author:** [@jvellojin](https://community.freefem.org/u/jvellojin)\ **Replies:** 2\ **Last updated:** [April 26, 2021, 6:00am UTC](https://community.freefem.org/t/adaptive-algorithm-using-blue-green-marking-strategy/943 "2021-04-26T06:00:02Z")
Dear Freefem community. I wonder if there is any way to implement the blue-green adaptive refinement strategy using Adaptmesh: Start with a coarse mesh Th Solve a discrete problem in the actual mesh Th Compute eta\_K f… --- ## [WiFi Propagation example errors](https://community.freefem.org/t/wifi-propagation-example-errors/941)
**Author:** [@LiudasD](https://community.freefem.org/u/LiudasD)\ **Replies:** 2\ **Last updated:** [April 25, 2021, 8:01am UTC](https://community.freefem.org/t/wifi-propagation-example-errors/941 "2021-04-25T08:01:08Z")
Hello, I’m trying to execute example from Wifi Propagation, but I get errors: Error umpfack umfpack\_zi\_numeric status 1 Error umfpack\_di\_solve status 1 -- Solve : min (-0.13597,-0.169774) max (1,0.… --- ## [Save fields under binary format](https://community.freefem.org/t/save-fields-under-binary-format/939)
**Author:** [@adrienrvr](https://community.freefem.org/u/adrienrvr)\ **Replies:** 3\ **Last updated:** [April 23, 2021, 1:43pm UTC](https://community.freefem.org/t/save-fields-under-binary-format/939 "2021-04-23T13:43:23Z")
Hi every one, I would like to export my data under binary format. I use {ofstream export(“BF\_binary.btxt”, binary); export \<\< Ux \<\< endl; export \<\< Rd1 \<\< endl; } but the resulting file BF\_binary.btxt is not a bi… --- ## [Laplace eigenproblem with Robin boundary condition](https://community.freefem.org/t/laplace-eigenproblem-with-robin-boundary-condition/895)
**Author:** [@m-schindler](https://community.freefem.org/u/m-schindler)\ **Replies:** 16\ **Last updated:** [April 23, 2021, 1:33pm UTC](https://community.freefem.org/t/laplace-eigenproblem-with-robin-boundary-condition/895 "2021-04-23T13:33:06Z")
Dear FreeFem users and developers, I need to solve the eigenequation of the Laplace operator in two spatial dimensions, with a homogeneous Robin boundary condition: Laplace phi = lambda phi in the domain a phi… --- ## [How to add Ffmatlib](https://community.freefem.org/t/how-to-add-ffmatlib/852)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 1\ **Last updated:** [March 15, 2021, 3:23pm UTC](https://community.freefem.org/t/how-to-add-ffmatlib/852 "2021-03-15T15:23:35Z")
Hello, I need to use ffmatlib to sava my data in text format. I am using Atom editor for windows and I search Ffmatlib package to install, but I can not find this package to install. So may you help me how to install t… --- ## [Boundary labels](https://community.freefem.org/t/boundary-labels/938)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 2\ **Last updated:** [April 22, 2021, 9:33am UTC](https://community.freefem.org/t/boundary-labels/938 "2021-04-22T09:33:39Z")
Hi all, I realise we can loop over triangles, and print Th(i).label so that know which nodes are at boundaries. However, if we use of P2 element, and loop over degrees of freedom such as: for(int i=0; i\ **Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 2\ **Last updated:** [April 22, 2021, 9:12am UTC](https://community.freefem.org/t/one-dimensional-model/936 "2021-04-22T09:12:41Z") Dear all, I can understand FreeFEM++ does not have 1D FEM space. However, is there a trick that can sort of implement a one-dimensional structure. For example, considering a 1D wire (or a beam) interacting with a 3D flo… --- ## [Impose boundary conditions](https://community.freefem.org/t/impose-boundary-conditions/923)
**Author:** [@Emma87](https://community.freefem.org/u/Emma87)\ **Replies:** 2\ **Last updated:** [April 21, 2021, 4:17pm UTC](https://community.freefem.org/t/impose-boundary-conditions/923 "2021-04-21T16:17:09Z")
Hi everyone! I want to know how I can impose Dirichlet boundary condition on \\Gamma\_ {E2} a different value than in the cases !mesh|690x365 Gamma\_ {E3} = \\Gamma\_ {E1} \< \\Gamma\_ {E2}, in FreeFem. Is there an example of h… --- ## [Coarse space Error](https://community.freefem.org/t/coarse-space-error/931)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 0\ **Last updated:** [April 19, 2021, 4:25pm UTC](https://community.freefem.org/t/coarse-space-error/931 "2021-04-19T16:25:25Z")
Hello developer, In defining a coarse space by ’ int mysplit = 3; mesh3 Thc = trunc(Th, 1, split = mysplit); ’ when I increase mysplit to a value \> 1 , I get below error; may you help me what is the problem? ORAS TWO-… --- ## [How to make the vibration of the 3D square plate's equation in Freefem?](https://community.freefem.org/t/how-to-make-the-vibration-of-the-3d-square-plates-equation-in-freefem/934)
**Author:** [@HGH](https://community.freefem.org/u/HGH)\ **Replies:** 0\ **Last updated:** [April 20, 2021, 2:20am UTC](https://community.freefem.org/t/how-to-make-the-vibration-of-the-3d-square-plates-equation-in-freefem/934 "2021-04-20T02:20:09Z")
Hello, everybody I want to ask how to write the vibration of the 3D square plate’s equation such like Matlab’s, I don’t know the Freefem’s vibration PDE is how to write, and I confused for a long time. I would appreciat… --- ## [How to setup the simple supported condition on a 3D plate by Freefem?](https://community.freefem.org/t/how-to-setup-the-simple-supported-condition-on-a-3d-plate-by-freefem/915)
**Author:** [@HGH](https://community.freefem.org/u/HGH)\ **Replies:** 1\ **Last updated:** [April 20, 2021, 2:05am UTC](https://community.freefem.org/t/how-to-setup-the-simple-supported-condition-on-a-3d-plate-by-freefem/915 "2021-04-20T02:05:34Z")
Hello ,guys who know how to setup the simple supported condition on a 3D plate by Freefem? --- ## [GetARGV & Elapsed time](https://community.freefem.org/t/getargv-elapsed-time/930)
**Author:** [@Dua](https://community.freefem.org/u/Dua)\ **Replies:** 1\ **Last updated:** [April 20, 2021, 2:01am UTC](https://community.freefem.org/t/getargv-elapsed-time/930 "2021-04-20T02:01:07Z")
Hello all, I have a problem with GetARGV definition, like in this script ‘int vdebug = getARGV("-d", 1);’ the value 1 is related to d or to vdeug? My other question is that how can I see the total elapsed time for run… --- ## [Gsl interpolation in 2d](https://community.freefem.org/t/gsl-interpolation-in-2d/928)
**Author:** [@balajek](https://community.freefem.org/u/balajek)\ **Replies:** 1\ **Last updated:** [April 19, 2021, 2:00pm UTC](https://community.freefem.org/t/gsl-interpolation-in-2d/928 "2021-04-19T14:00:35Z")
Hi, Does FreeFem have the gsl plugin for gsl\_spline2d, similar to gslspline? https://www.gnu.org/software/gsl/doc/html/interp.html#id4 Thanks and Regards, Balaje --- ## [Interpolate between local non-overlap mesh to local overlap mesh](https://community.freefem.org/t/interpolate-between-local-non-overlap-mesh-to-local-overlap-mesh/925)
**Author:** [@KBarrett](https://community.freefem.org/u/KBarrett)\ **Replies:** 6\ **Last updated:** [April 16, 2021, 8:53pm UTC](https://community.freefem.org/t/interpolate-between-local-non-overlap-mesh-to-local-overlap-mesh/925 "2021-04-16T20:53:10Z")
Hello FF community, I have created two sets of local meshes: one where there is overlap and one with no overlap, and I’m using ffddmbuildDmesh function to create my decomposed mesh. I need a local mesh with no overlap t… --- ## [Boundary condition on mesh](https://community.freefem.org/t/boundary-condition-on-mesh/911)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 2\ **Last updated:** [April 15, 2021, 3:15pm UTC](https://community.freefem.org/t/boundary-condition-on-mesh/911 "2021-04-15T15:15:40Z")
Dear all, I only have mesh imported from a TetGen output. How should I enforce the boundary conditions in this case (the corresponding boundary nodes are labelled)? Thank you in advance! Yongxing --- ## [Loops with else](https://community.freefem.org/t/loops-with-else/916)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 1\ **Last updated:** [April 15, 2021, 7:53am UTC](https://community.freefem.org/t/loops-with-else/916 "2021-04-15T07:53:43Z")
Hi, i want to write following conditions with FF++: we suppose that a1\a1)&(t\ a1) & (t\>a2) {…instr… --- ## [Identifying 3D domain boundaries](https://community.freefem.org/t/identifying-3d-domain-boundaries/908)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 4\ **Last updated:** [April 14, 2021, 9:27am UTC](https://community.freefem.org/t/identifying-3d-domain-boundaries/908 "2021-04-14T09:27:58Z")
Hello Everyone, Can anyone suggest me for accessing a particular boundary of 3d shaped problem domain? in the case of the unit cube box, how the numbering starts for boundaries here. --- ## [How can I get the basis function of an existing finite element space or to build a finite element space according to my existing basis functions?](https://community.freefem.org/t/how-can-i-get-the-basis-function-of-an-existing-finite-element-space-or-to-build-a-finite-element-space-according-to-my-existing-basis-functions/914)
**Author:** [@Duzi100](https://community.freefem.org/u/Duzi100)\ **Replies:** 0\ **Last updated:** [April 14, 2021, 8:37am UTC](https://community.freefem.org/t/how-can-i-get-the-basis-function-of-an-existing-finite-element-space-or-to-build-a-finite-element-space-according-to-my-existing-basis-functions/914 "2021-04-14T08:37:21Z")
Dear all， At present，I‘m going to deal with the basis function using a spacial algorithm to realize optimizing finite element method， so I’m facing the following two challenges： （1）With knowing mesh “TH” ，I can use the… --- ## [Question -error estimate finite elements](https://community.freefem.org/t/question-error-estimate-finite-elements/910)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 0\ **Last updated:** [April 13, 2021, 9:21am UTC](https://community.freefem.org/t/question-error-estimate-finite-elements/910 "2021-04-13T09:21:05Z")
Hello, This is not an explicit FreeFEM question, but I hope you can indicate some useful reference, since it deals with the precision of the finite element method when the boundary condition changes. Suppose we have a … --- ## [Import finite difference field to FreeFem](https://community.freefem.org/t/import-finite-difference-field-to-freefem/907)
**Author:** [@sgkkr](https://community.freefem.org/u/sgkkr)\ **Replies:** 0\ **Last updated:** [April 12, 2021, 2:42pm UTC](https://community.freefem.org/t/import-finite-difference-field-to-freefem/907 "2021-04-12T14:42:38Z")
I have a finite-difference 1-dimensional velocity field which I want to import to FreeFem. I perform the following task on FreeFem to record the velocity field in tempx. Wh tempx; { ifstream file(“velfield.txt”); fil… --- ## [Libmpifort.so.12: undefined symbol: MPI\_UNWEIGHTED](https://community.freefem.org/t/libmpifort-so-12-undefined-symbol-mpi-unweighted/900)
**Author:** [@jeyc](https://community.freefem.org/u/jeyc)\ **Replies:** 6\ **Last updated:** [April 12, 2021, 7:53am UTC](https://community.freefem.org/t/libmpifort-so-12-undefined-symbol-mpi-unweighted/900 "2021-04-12T07:53:13Z")
Hello, I have installed FreeFem++ 4.8. When I run this command: /usr/local/share/freefem++/4.8/bin/ff-mpirun -np 2 mesh.edp I get this error: /usr/local/share/freefem++/4.8/bin/FreeFem+±mpi: symbol lookup error: /usr… --- ## [About how to use the lame formula with time domain for 3D plate](https://community.freefem.org/t/about-how-to-use-the-lame-formula-with-time-domain-for-3d-plate/905)
**Author:** [@HGH](https://community.freefem.org/u/HGH)\ **Replies:** 0\ **Last updated:** [April 12, 2021, 7:05am UTC](https://community.freefem.org/t/about-how-to-use-the-lame-formula-with-time-domain-for-3d-plate/905 "2021-04-12T07:05:02Z")
Hello, guys Regarding how to use the lame formula (elasiticity) to simulate a 1m x 0.5m x 0.002m plate, the condition of the plate is a simple support condition, and the internal grid of the plate is a tetrahedron, and … --- ## [How to compare the same function on different meshes](https://community.freefem.org/t/how-to-compare-the-same-function-on-different-meshes/904)
**Author:** [@dajopez](https://community.freefem.org/u/dajopez)\ **Replies:** 0\ **Last updated:** [April 11, 2021, 3:35am UTC](https://community.freefem.org/t/how-to-compare-the-same-function-on-different-meshes/904 "2021-04-11T03:35:16Z")
Hello, To test accuracy, I would like to solve the same differential equation on different meshes and then compute the difference as integrals. Can I just naively subtract the two functions or do I need to do additional… --- ## [Problems with chdir](https://community.freefem.org/t/problems-with-chdir/902)
**Author:** [@RaMattoso](https://community.freefem.org/u/RaMattoso)\ **Replies:** 4\ **Last updated:** [April 9, 2021, 5:15pm UTC](https://community.freefem.org/t/problems-with-chdir/902 "2021-04-09T17:15:59Z")
Hello fellows, I’m new using FreeFeem, but I think the thing I’m trying to do is so simple. The code is exec("mkdir result"); exec("chdir result"); ofstream teste("teste.txt"); teste \<\< "hello World!"; exec("cd ..")… --- ## [How to use ternary operator for assigning a function](https://community.freefem.org/t/how-to-use-ternary-operator-for-assigning-a-function/896)
**Author:** [@arousta](https://community.freefem.org/u/arousta)\ **Replies:** 4\ **Last updated:** [April 8, 2021, 7:15pm UTC](https://community.freefem.org/t/how-to-use-ternary-operator-for-assigning-a-function/896 "2021-04-08T19:15:12Z")
I want to do a function dispatch like below: func real a(real s) {return s\*s; } func real c(real s) {return s-1; } func myf = true ? a : c; of course I want to use something other than true for the condition. But I… --- ## [Regions permittivity](https://community.freefem.org/t/regions-permittivity/830)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 8\ **Last updated:** [March 10, 2021, 3:46pm UTC](https://community.freefem.org/t/regions-permittivity/830 "2021-03-10T15:46:29Z")
Hello colleagues, I have a domain with two different regions ( region 1 and region 2). I need to define a function for permittivity so that in region 1 it considers the permittivity of air but in the region 2 another pe… --- ## [Importing a profile to set as the BC](https://community.freefem.org/t/importing-a-profile-to-set-as-the-bc/891)
**Author:** [@zese](https://community.freefem.org/u/zese)\ **Replies:** 0\ **Last updated:** [April 5, 2021, 7:12pm UTC](https://community.freefem.org/t/importing-a-profile-to-set-as-the-bc/891 "2021-04-05T19:12:54Z")
Dear all, I have a data file containing a velocity profile of y and u(y) in which y and u are array of size 126. I want to import this text file to freefem and set it as the inlet boundary condition (x=0,y=y). how can I… --- ## [Invalide array size](https://community.freefem.org/t/invalide-array-size/890)
**Author:** [@Robert](https://community.freefem.org/u/Robert)\ **Replies:** 2\ **Last updated:** [April 5, 2021, 1:25pm UTC](https://community.freefem.org/t/invalide-array-size/890 "2021-04-05T13:25:30Z")
Hello again, I have the following lines: \> load "SLEPc-complex" \> include "macro\_ddm.idp" \> \> mesh Th=readmesh("D:\\\\Test\\\\Mesh.msh"); \> plot (Th, cmm="Mesh.msh", wait=true); \> \> func E = \[P2, P2, P2, P1\]; \> fespac… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=60) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=62)