# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=57 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 58 --- ## [Textile/Cloth Simulation](https://community.freefem.org/t/textile-cloth-simulation/1158)
**Author:** [@udikon](https://community.freefem.org/u/udikon)\ **Replies:** 0\ **Last updated:** [August 15, 2021, 4:00pm UTC](https://community.freefem.org/t/textile-cloth-simulation/1158 "2021-08-15T16:00:39Z")
Hi Community, did anyone simulate textile using FreeFem? E.g. dropping a piece of textile/cloth on a solid surface. --- ## [Evolution equation without x](https://community.freefem.org/t/evolution-equation-without-x/1156)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [August 15, 2021, 9:36am UTC](https://community.freefem.org/t/evolution-equation-without-x/1156 "2021-08-15T09:36:57Z")
Hi, is it possible to resolve with FF++ equation depending only on time t and not depending on x. For example, what’s formulation we have to use to find u(t) solution of the equation du/dt =a\*u ? Regards --- ## [Stall in some multi-node parallel calculations](https://community.freefem.org/t/stall-in-some-multi-node-parallel-calculations/1143)
**Author:** [@etj](https://community.freefem.org/u/etj)\ **Replies:** 83\ **Last updated:** [August 14, 2021, 1:42pm UTC](https://community.freefem.org/t/stall-in-some-multi-node-parallel-calculations/1143 "2021-08-14T13:42:32Z")
Hello, I am trying to solve some problem in parallel, with FreeFem++ 4.9 installed on a cluster, where each node has 2 Intel Broadwell processors with 14 cores, and either 128 or 256 GB of RAM. Everything works fine wh… --- ## [Object is in wrong state](https://community.freefem.org/t/object-is-in-wrong-state/1145)
**Author:** [@Mik](https://community.freefem.org/u/Mik)\ **Replies:** 5\ **Last updated:** [August 13, 2021, 8:57am UTC](https://community.freefem.org/t/object-is-in-wrong-state/1145 "2021-08-13T08:57:19Z")
Dear members, I have stumbled upon a Petsc error. Out of my full mesh, I am trying to solve the heat transfer problem on selected volume numbers defined as reg. Apart from these volume numbers, the rest are not solving… --- ## [Array does not store correct values](https://community.freefem.org/t/array-does-not-store-correct-values/1155)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 2\ **Last updated:** [August 13, 2021, 8:15am UTC](https://community.freefem.org/t/array-does-not-store-correct-values/1155 "2021-08-13T08:15:33Z")
Could somebody please explain why real\[int, int\] IDeviatoric = \[\[2/3, -1/3, -1/3, 0, 0, 0\], \[-1/3, 2/3, -1/3, 0, 0, 0\], \[-1/3, -1/3, 2/3, 0… --- ## [Solving complex PDEs](https://community.freefem.org/t/solving-complex-pdes/1154)
**Author:** [@zese](https://community.freefem.org/u/zese)\ **Replies:** 0\ **Last updated:** [August 12, 2021, 12:56pm UTC](https://community.freefem.org/t/solving-complex-pdes/1154 "2021-08-12T12:56:55Z")
Dear all I have a PDE equation with complex values. Should I solve it by Matrix inversion or using solve is enough? Best regards --- ## [Fourth order derivative Help](https://community.freefem.org/t/fourth-order-derivative-help/1150)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 0\ **Last updated:** [August 11, 2021, 7:59am UTC](https://community.freefem.org/t/fourth-order-derivative-help/1150 "2021-08-11T07:59:04Z")
Hello Everyone error message appearing for third or fourth order derivatives. e.g. for u\_xxx I have written dxxx(u) but it is showing identifier does not exist. Help me to fix it. --- ## [Define another complicated function](https://community.freefem.org/t/define-another-complicated-function/1129)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 1\ **Last updated:** [August 6, 2021, 3:26pm UTC](https://community.freefem.org/t/define-another-complicated-function/1129 "2021-08-06T15:26:05Z")
Hi, real x1=0.0; real I1=I(x1,t)-0.5; where I is the solution of an system My question is: in FF++ how we define the function I1? Please. The difficulties is that FF++ don’t understant I(x1,t) Thank you for the hel… --- ## [Applying a modified preconditioner matrix in PETSc](https://community.freefem.org/t/applying-a-modified-preconditioner-matrix-in-petsc/1142)
**Author:** [@gbwalton](https://community.freefem.org/u/gbwalton)\ **Replies:** 4\ **Last updated:** [August 6, 2021, 2:58pm UTC](https://community.freefem.org/t/applying-a-modified-preconditioner-matrix-in-petsc/1142 "2021-08-06T14:58:06Z")
Hi all, Is it possible to specific a modified preconditioner matrix when using PETSc in FreeFEM? In PETSc a different Amat and Pmat can be specified using KSPSetOperators(KSP ksp,Mat Amat,Mat Pmat). Is this possible us… --- ## ["transfer" in PETSc-complex interface](https://community.freefem.org/t/transfer-in-petsc-complex-interface/1140)
**Author:** [@yuki](https://community.freefem.org/u/yuki)\ **Replies:** 2\ **Last updated:** [August 6, 2021, 5:38am UTC](https://community.freefem.org/t/transfer-in-petsc-complex-interface/1140 "2021-08-06T05:38:59Z")
Dear all, I would like to use “transfer” function in PETSc-complex interface. In FreeFEM v 4.8, the following code worked well: //load “PETSc” load “PETSc-complex” macro dimension()2// EOM include “macro\_ddm.idp” m… --- ## [Immersed FEM/Boundary Method, cutFEM](https://community.freefem.org/t/immersed-fem-boundary-method-cutfem/1138)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [August 4, 2021, 4:47pm UTC](https://community.freefem.org/t/immersed-fem-boundary-method-cutfem/1138 "2021-08-04T16:47:45Z")
Has anyone implemented Immersed FEM method or cutFEM method in FreeFem? Is there an example? --- ## [Resolve an equation](https://community.freefem.org/t/resolve-an-equation/1134)
**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\ **Replies:** 0\ **Last updated:** [August 3, 2021, 9:58am UTC](https://community.freefem.org/t/resolve-an-equation/1134 "2021-08-03T09:58:06Z")
Hi, i hope that you can help me to solve my problem please. I(x,t) is solution of a variational formulation: system. To find I, we write load “iovtk” verbosity=1; int Nbx=10000; real L=2.; real t=0.0; real dt=0.… --- ## [Function returning multiple arguments of different types](https://community.freefem.org/t/function-returning-multiple-arguments-of-different-types/1135)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 0\ **Last updated:** [August 3, 2021, 10:55am UTC](https://community.freefem.org/t/function-returning-multiple-arguments-of-different-types/1135 "2021-08-03T10:55:18Z")
Hi, So I have a function, but I would need that function to return multiple arguments (sort of like pointers work in C++ code). For example assume a function func real\[int\] foo(real fooReal, bool\[int\] fooBoolArray, re… --- ## [Assertion fail:(ie==nbe) in msh2.cpp](https://community.freefem.org/t/assertion-fail-ie-nbe-in-msh2-cpp/1133)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 2\ **Last updated:** [August 2, 2021, 6:01pm UTC](https://community.freefem.org/t/assertion-fail-ie-nbe-in-msh2-cpp/1133 "2021-08-02T18:01:21Z")
Dear all, I have a 3D mesh generated by GID, which has an internal surface as shown in the following figure. Using one processor there is no problem of reading the mesh and executing my parallel code. However, the code… --- ## [Docomposed mesh visualization](https://community.freefem.org/t/docomposed-mesh-visualization/1122)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 1\ **Last updated:** [July 29, 2021, 12:36pm UTC](https://community.freefem.org/t/docomposed-mesh-visualization/1122 "2021-07-29T12:36:50Z")
Hello, I need to visualize my 3D mesh that is decomposed to n subdomains in a single image, purpose is to show construction of subdomains, I used ‘medit(“Th”+mpirank, MThi);’ but it shows each subdomain separately. how… --- ## [2D boundary of a cube](https://community.freefem.org/t/2d-boundary-of-a-cube/1119)
**Author:** [@simonenatipoltri](https://community.freefem.org/u/simonenatipoltri)\ **Replies:** 1\ **Last updated:** [July 29, 2021, 10:32am UTC](https://community.freefem.org/t/2d-boundary-of-a-cube/1119 "2021-07-29T10:32:18Z")
Hi there, I’ve constructed a cube in such a way load “msh3” int\[int\] ll= \[1,2,1,2,3,4\]; mesh3 Th = cube(20,20,20,label=ll); how do I introduce a 2D mesh defined as one of the faces of the cube? Is it possible to use … --- ## [Enquiry about support of FreeFEM](https://community.freefem.org/t/enquiry-about-support-of-freefem/1121)
**Author:** [@pratik31](https://community.freefem.org/u/pratik31)\ **Replies:** 1\ **Last updated:** [July 28, 2021, 7:28am UTC](https://community.freefem.org/t/enquiry-about-support-of-freefem/1121 "2021-07-28T07:28:36Z")
Hi all, I am new to this software. I want to know, does this software has a support for Isoparametric mapping Hybrid mesh (A mesh containing a combination of tri, quad, hexa elements) Parallel computing Can we solve a… --- ## [Iterative solution of the Navier-Stokes equation](https://community.freefem.org/t/iterative-solution-of-the-navier-stokes-equation/1116)
**Author:** [@aszaboa](https://community.freefem.org/u/aszaboa)\ **Replies:** 4\ **Last updated:** [July 26, 2021, 11:27am UTC](https://community.freefem.org/t/iterative-solution-of-the-navier-stokes-equation/1116 "2021-07-26T11:27:34Z")
Dear FreeFem users! I am interested in solving (a slightly modified form of the) Navier-Stokes equation, and I would like to test whether LU factorization or iterative solvers perform better. I have found some issues wh… --- ## [Installation problems on Windows](https://community.freefem.org/t/installation-problems-on-windows/1117)
**Author:** [@candy](https://community.freefem.org/u/candy)\ **Replies:** 0\ **Last updated:** [July 26, 2021, 8:00am UTC](https://community.freefem.org/t/installation-problems-on-windows/1117 "2021-07-26T08:00:00Z")
Hello! I am install the softeware on a new compute with win 10. But it gives the following error. Any comments and advice are welcome. Thank you in advance. --- ## [FreeFem PETSc matrix operations](https://community.freefem.org/t/freefem-petsc-matrix-operations/1109)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 5\ **Last updated:** [July 26, 2021, 7:29am UTC](https://community.freefem.org/t/freefem-petsc-matrix-operations/1109 "2021-07-26T07:29:05Z")
Is there a list of all the PETSc matrix operations implemented in FreeFem? such as, addition, minus, times by a constant, copy a matrix, and so on? --- ## [Unused parallel \`createMat\` leads to more efficiency but wrong results](https://community.freefem.org/t/unused-parallel-createmat-leads-to-more-efficiency-but-wrong-results/1115)
**Author:** [@Ionizing](https://community.freefem.org/u/Ionizing)\ **Replies:** 3\ **Last updated:** [July 24, 2021, 11:50am UTC](https://community.freefem.org/t/unused-parallel-createmat-leads-to-more-efficiency-but-wrong-results/1115 "2021-07-24T11:50:41Z")
Hi all, I’m using FF to solve an eigenproblem but I have come across some problems with SLEPc. Problem I’d like to solve the Hydrogen atom electron wave function and I’ve done it with a coarse mesh grid (40x40x40). But… --- ## [Multi region 3dmesh](https://community.freefem.org/t/multi-region-3dmesh/1108)
**Author:** [@niaa](https://community.freefem.org/u/niaa)\ **Replies:** 1\ **Last updated:** [July 23, 2021, 7:00am UTC](https://community.freefem.org/t/multi-region-3dmesh/1108 "2021-07-23T07:00:27Z")
Hello everyone, I wanna make a mesh with 3 different regions. The region label for two of them is well defined. I need to say for example: if the region is equal to 1 keep it as 1 ; if the region is equal to 2 keep it … --- ## [Weighting integral by mesh area](https://community.freefem.org/t/weighting-integral-by-mesh-area/1114)
**Author:** [@zese](https://community.freefem.org/u/zese)\ **Replies:** 0\ **Last updated:** [July 23, 2021, 6:51am UTC](https://community.freefem.org/t/weighting-integral-by-mesh-area/1114 "2021-07-23T06:51:37Z")
Dear all, I have an integral as int2d(th)(u\*.v) in which \* is the complex conjugate and I want it for normalizing u=u/ int2d(th)(u\*.v) . I want to weight it by element size. I am not sure when I write it simply as int2… --- ## [Problems in solving hydrogen atom energy levels](https://community.freefem.org/t/problems-in-solving-hydrogen-atom-energy-levels/1110)
**Author:** [@Ionizing](https://community.freefem.org/u/Ionizing)\ **Replies:** 3\ **Last updated:** [July 22, 2021, 10:49am UTC](https://community.freefem.org/t/problems-in-solving-hydrogen-atom-energy-levels/1110 "2021-07-22T10:49:43Z")
Hi, it’s me again. Problem I want to solve the hydrogen atom using FF. The eigenvalue problem is like I built a cylinder mesh (r = 15A, h = 30A) as the FE space: Then defined the problem via varf a(u1, u2) = … --- ## [Segmentation Violation using PETSc](https://community.freefem.org/t/segmentation-violation-using-petsc/1097)
**Author:** [@marcodeba](https://community.freefem.org/u/marcodeba)\ **Replies:** 14\ **Last updated:** [July 22, 2021, 10:18am UTC](https://community.freefem.org/t/segmentation-violation-using-petsc/1097 "2021-07-22T10:18:38Z")
Dear FreeFem developers and users, I’m writing you since I’m having some troubles once I am required to pass from local to global solution in my parallel script. I have an algorithm that is fine in sequential and is app… --- ## [How the boundary condition is calculated](https://community.freefem.org/t/how-the-boundary-condition-is-calculated/1113)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 0\ **Last updated:** [July 22, 2021, 9:36am UTC](https://community.freefem.org/t/how-the-boundary-condition-is-calculated/1113 "2021-07-22T09:36:14Z")
Dear all, I am wondering how FreeFem imposes the Dirichlet boundary condition when using tgv= -1? I have tried both the direct solver LU and iterative solver hypre, why it’s not exactly zero at the wall boundary as sho… --- ## [How to save/storage solutions in Freefem](https://community.freefem.org/t/how-to-save-storage-solutions-in-freefem/1111)
**Author:** [@lietvo](https://community.freefem.org/u/lietvo)\ **Replies:** 0\ **Last updated:** [July 21, 2021, 5:34pm UTC](https://community.freefem.org/t/how-to-save-storage-solutions-in-freefem/1111 "2021-07-21T17:34:20Z")
Hello everyone, I am using Freefem to solve the time dependent Stokes equations with the implicit Euler and FEM. My goal is computing the errors at each time step. When we know the analytical solutions, the problem is e… --- ## [The type "9" of cell of the "vtk" can not be input in FreeFem](https://community.freefem.org/t/the-type-9-of-cell-of-the-vtk-can-not-be-input-in-freefem/1098)
**Author:** [@HGH](https://community.freefem.org/u/HGH)\ **Replies:** 4\ **Last updated:** [July 21, 2021, 7:37am UTC](https://community.freefem.org/t/the-type-9-of-cell-of-the-vtk-can-not-be-input-in-freefem/1098 "2021-07-21T07:37:23Z")
Dear all, I have many results of “vtk” file from the other fluid software, and I need to input these “vtk” files into my FreeFEM++ programs to calculate next step. The mesh of “vtk” is two dimensional, and the cell type… --- ## [What are the best way to get error estimates from a PDE solver?](https://community.freefem.org/t/what-are-the-best-way-to-get-error-estimates-from-a-pde-solver/1086)
**Author:** [@dajopez](https://community.freefem.org/u/dajopez)\ **Replies:** 13\ **Last updated:** [July 21, 2021, 7:32am UTC](https://community.freefem.org/t/what-are-the-best-way-to-get-error-estimates-from-a-pde-solver/1086 "2021-07-21T07:32:16Z")
Hello, I am solving eigenfunctions on a simple domain and I want to get some nice error and convergence data from it. What are the best ways to do this? Are there any quick commands in FreeFEM to get it done automatical… --- ## [Reset the Dirichelet boundary condition](https://community.freefem.org/t/reset-the-dirichelet-boundary-condition/1104)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 1\ **Last updated:** [July 19, 2021, 3:17pm UTC](https://community.freefem.org/t/reset-the-dirichelet-boundary-condition/1104 "2021-07-19T15:17:47Z")
Dear all, Is the an example about resetting the Dirichlet boundary condition after modifying a PETSc matrix? For example, Mat A; A=a(Vh, Vh, tgv=-1); rhs=a(0,Vh, tgv=-1); a modification of A and rhs; We then need … [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=56) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=58)