# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=34 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 35 --- ## [Second derivative of right cauchy-green tensor in freefem](https://community.freefem.org/t/second-derivative-of-right-cauchy-green-tensor-in-freefem/2355)
**Author:** [@yhao](https://community.freefem.org/u/yhao)\ **Replies:** 0\ **Last updated:** [March 24, 2023, 12:12am UTC](https://community.freefem.org/t/second-derivative-of-right-cauchy-green-tensor-in-freefem/2355 "2023-03-24T00:12:28Z")
Dear All, I am working on 3D compressible neo-hookean solid with Freefem. I searched and got this 2D example from the forum (from Simulating neo-hookean material) and here is the code provided: ElasticLaw2d.idp (2.9 KB… --- ## [PETSc Error: Local columns of A10 do not equal local rows of A00 with Non conforming Finite Element](https://community.freefem.org/t/petsc-error-local-columns-of-a10-do-not-equal-local-rows-of-a00-with-non-conforming-finite-element/2353)
**Author:** [@Loic](https://community.freefem.org/u/Loic)\ **Replies:** 8\ **Last updated:** [March 23, 2023, 2:37pm UTC](https://community.freefem.org/t/petsc-error-local-columns-of-a10-do-not-equal-local-rows-of-a00-with-non-conforming-finite-element/2353 "2023-03-23T14:37:35Z")
Hello all, Inspired by what I have found on the FreeFEM git repo, I am solving Stokes equation in 3D in parallel using a fieldsplit preconditioner. I note my vectorial FE Pk4 = \[PkV, PkV, PkV, PkM\] where PkV is the… --- ## [Adaptive FEM about adaptmesh](https://community.freefem.org/t/adaptive-fem-about-adaptmesh/2354)
**Author:** [@Kellen](https://community.freefem.org/u/Kellen)\ **Replies:** 0\ **Last updated:** [March 23, 2023, 8:55am UTC](https://community.freefem.org/t/adaptive-fem-about-adaptmesh/2354 "2023-03-23T08:55:34Z")
Hi, everyone! I want to know whether the function adpatmesh in freefem++ can adapt the specific elements based on the initial mesh fixed or not. That is to say, can AdaptMesh refine mesh cells that meet certain error req… --- ## [Brain mesh or Breast mesh](https://community.freefem.org/t/brain-mesh-or-breast-mesh/2351)
**Author:** [@lassounon](https://community.freefem.org/u/lassounon)\ **Replies:** 2\ **Last updated:** [March 22, 2023, 10:32pm UTC](https://community.freefem.org/t/brain-mesh-or-breast-mesh/2351 "2023-03-22T22:32:43Z")
Hello community I would like someone to share with me a 2D mesh of the human brain and/or breast. I would like to test a code on these types of domain. I haven’t seen an example in the freefem++ documentation. THANKS. --- ## [Rotational periodicity](https://community.freefem.org/t/rotational-periodicity/2352)
**Author:** [@Markov](https://community.freefem.org/u/Markov)\ **Replies:** 0\ **Last updated:** [March 22, 2023, 2:03pm UTC](https://community.freefem.org/t/rotational-periodicity/2352 "2023-03-22T14:03:27Z")
Hello, I was wondering if there is a way to enforce a rotational periodic boundary condition to two patches. Thank you --- ## [Suppress or turn off degrees of freedom](https://community.freefem.org/t/suppress-or-turn-off-degrees-of-freedom/2344)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 3\ **Last updated:** [March 22, 2023, 12:28pm UTC](https://community.freefem.org/t/suppress-or-turn-off-degrees-of-freedom/2344 "2023-03-22T12:28:04Z")
Dear all, How can we set the degrees of freedom to be 0 in a region (similar to a boundary condition)? or turn off so that this region would not be assembled? Thank you in advance! --- ## [How to impose Dirichlet boundary conditions by Lagrange multipliers](https://community.freefem.org/t/how-to-impose-dirichlet-boundary-conditions-by-lagrange-multipliers/2330)
**Author:** [@zhugp123](https://community.freefem.org/u/zhugp123)\ **Replies:** 3\ **Last updated:** [March 22, 2023, 11:03am UTC](https://community.freefem.org/t/how-to-impose-dirichlet-boundary-conditions-by-lagrange-multipliers/2330 "2023-03-22T11:03:08Z")
Hi, I want to impose Dirichlet boundary conditions by using the Lagrange multiplier method. The governing equation for heat transfer is \\Delta T = 0, where T is the temperature. The boundary conditions are shown in th… --- ## [Incompatible boundary conditions in parallel FreeFEM](https://community.freefem.org/t/incompatible-boundary-conditions-in-parallel-freefem/2347)
**Author:** [@fagnelli](https://community.freefem.org/u/fagnelli)\ **Replies:** 1\ **Last updated:** [March 22, 2023, 6:02am UTC](https://community.freefem.org/t/incompatible-boundary-conditions-in-parallel-freefem/2347 "2023-03-22T06:02:40Z")
Hi, I am trying to test FreeFem parallel (combined with PETSc) by solving the following linear elastic problem: a 2D truss is clamped at the left end and loaded at the right end with a surface force pointing downwards… --- ## [Brezzi-Douglas-Marini face element in 3D](https://community.freefem.org/t/brezzi-douglas-marini-face-element-in-3d/2349)
**Author:** [@candy](https://community.freefem.org/u/candy)\ **Replies:** 0\ **Last updated:** [March 22, 2023, 2:53am UTC](https://community.freefem.org/t/brezzi-douglas-marini-face-element-in-3d/2349 "2023-03-22T02:53:17Z")
Hello everyone, I want to use the Brezzi-Douglas-Marini face element rather than the Raviart-Thomas face element in 3D. Could you tell me how to use it? Thanks in advance. --- ## [Fail with a very basic 3d mesh](https://community.freefem.org/t/fail-with-a-very-basic-3d-mesh/2348)
**Author:** [@mrbenson](https://community.freefem.org/u/mrbenson)\ **Replies:** 0\ **Last updated:** [March 21, 2023, 5:28pm UTC](https://community.freefem.org/t/fail-with-a-very-basic-3d-mesh/2348 "2023-03-21T17:28:59Z")
Hi, I just tried a very simple 3d steady-state thermal problem : two solids, each has a specific thermal conductivity two mixed boundary conditions for each thermal space has a specific conductance hi and an external … --- ## [Navier Boundary Condtion for Stokes equation](https://community.freefem.org/t/navier-boundary-condtion-for-stokes-equation/2309)
**Author:** [@zhugp123](https://community.freefem.org/u/zhugp123)\ **Replies:** 5\ **Last updated:** [March 20, 2023, 2:11am UTC](https://community.freefem.org/t/navier-boundary-condtion-for-stokes-equation/2309 "2023-03-20T02:11:03Z")
I am learning the document written by Prof. Frederic Hecht on boundary conditions for the Stokes equation. I have a question about the Navier boundary condition. How the following equation is derived, especially th… --- ## [FreeFem Courses: Recommendations for Learning](https://community.freefem.org/t/freefem-courses-recommendations-for-learning/1391)
**Author:** [@willrey](https://community.freefem.org/u/willrey)\ **Replies:** 7\ **Last updated:** [March 19, 2023, 8:57am UTC](https://community.freefem.org/t/freefem-courses-recommendations-for-learning/1391 "2023-03-19T08:57:43Z")
Hi, I’ve been using FreeFem for several months, but I would ideally like to complete an online tutorial (e.g. Udemy/Coursera). Aside from the documentation on the FreeFem website, are there any courses which people woul… --- ## [Eigenvalues for schroedinger eqn - extremal and project out](https://community.freefem.org/t/eigenvalues-for-schroedinger-eqn-extremal-and-project-out/2339)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 5\ **Last updated:** [March 17, 2023, 8:46pm UTC](https://community.freefem.org/t/eigenvalues-for-schroedinger-eqn-extremal-and-project-out/2339 "2023-03-17T20:46:31Z")
I’m still trying to learn both FF and numerical methods details - initially I was going to do some EM problems but wanted to get a fun 3D geometry and had meshing issues. So, I backed up to 2D QM issue of interest . T… --- ## [Neumann boundary condition for discontinuous Galerkin](https://community.freefem.org/t/neumann-boundary-condition-for-discontinuous-galerkin/2338)
**Author:** [@kallol](https://community.freefem.org/u/kallol)\ **Replies:** 0\ **Last updated:** [March 16, 2023, 6:55am UTC](https://community.freefem.org/t/neumann-boundary-condition-for-discontinuous-galerkin/2338 "2023-03-16T06:55:50Z")
Dear all, I am trying to impose homogeneous Neumann boundary condition for discontinuous Galerkin method. But the int1d(…) command for the Neumann boundary condition is not working for discontinuous Galerkin case. It’… --- ## [Mesh error when combine two regions](https://community.freefem.org/t/mesh-error-when-combine-two-regions/2335)
**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\ **Replies:** 4\ **Last updated:** [March 15, 2023, 6:16pm UTC](https://community.freefem.org/t/mesh-error-when-combine-two-regions/2335 "2023-03-15T18:16:14Z")
Can someone spot the error: there is no problem to generate Thf and Ths, but there is an error to combine these to regions which is weird: Bug in mortar constrution : close to vertex 3 current line = 7 Assertion fail … --- ## [Why the plot function doesn't plot the velocity?](https://community.freefem.org/t/why-the-plot-function-doesnt-plot-the-velocity/2332)
**Author:** [@cfdyuewu](https://community.freefem.org/u/cfdyuewu)\ **Replies:** 2\ **Last updated:** [March 15, 2023, 6:11pm UTC](https://community.freefem.org/t/why-the-plot-function-doesnt-plot-the-velocity/2332 "2023-03-15T18:11:24Z")
the plot(\[uite1, uite2\], pite, coef=0.2, cmm=" \[Ux, Uy\] - p", WindowIndex=1); only plot the result of the first step, then it only plot the contour of the region, how to fix this?, the full code is load "iovtk" verb… --- ## [Problem on implementing fixed point method for nonlinear elliptic problem](https://community.freefem.org/t/problem-on-implementing-fixed-point-method-for-nonlinear-elliptic-problem/2322)
**Author:** [@AbuAzzan](https://community.freefem.org/u/AbuAzzan)\ **Replies:** 3\ **Last updated:** [March 14, 2023, 5:41pm UTC](https://community.freefem.org/t/problem-on-implementing-fixed-point-method-for-nonlinear-elliptic-problem/2322 "2023-03-14T17:41:06Z")
Hello freefem community, I am trying to solve a semilinear elliptic problem where the forcing term f(u) depends on the solution. Here I am using fixed point method implemented for nonlinear Schwarz method to solve the o… --- ## [Reduced dimension in the right hand side using levelset](https://community.freefem.org/t/reduced-dimension-in-the-right-hand-side-using-levelset/2329)
**Author:** [@jsmacd](https://community.freefem.org/u/jsmacd)\ **Replies:** 4\ **Last updated:** [March 13, 2023, 7:00pm UTC](https://community.freefem.org/t/reduced-dimension-in-the-right-hand-side-using-levelset/2329 "2023-03-13T19:00:31Z")
I’d like to implement a problem where the right-hand side integral is over a reduced dimension. I believe I want to implement the level sets argument, like I found under the heading “Problem Definition” : https://doc.fr… --- ## [ffmatlib3D and matlab](https://community.freefem.org/t/ffmatlib3d-and-matlab/2321)
**Author:** [@wanglongfei](https://community.freefem.org/u/wanglongfei)\ **Replies:** 6\ **Last updated:** [March 13, 2023, 4:47pm UTC](https://community.freefem.org/t/ffmatlib3d-and-matlab/2321 "2023-03-13T16:47:12Z")
Hello I’m sorry to bother you, I want to use ffmatlib3D to draw a cross-section of a 3D function, but I don’t know how to select the section. I want to know which parameters are used to select the section. Is it S1, S2,… --- ## [Trunc a mesh3 from a list of regions](https://community.freefem.org/t/trunc-a-mesh3-from-a-list-of-regions/2323)
**Author:** [@mrbenson](https://community.freefem.org/u/mrbenson)\ **Replies:** 2\ **Last updated:** [March 13, 2023, 4:44pm UTC](https://community.freefem.org/t/trunc-a-mesh3-from-a-list-of-regions/2323 "2023-03-13T16:44:21Z")
Hello, Is it possible to extend the truncfunction with an array region as argument ? It could be useful to write trunc(Th,region=listRegion or trunc(Th,region=\[region1,region2\] instead of writing the conditional test… --- ## [How to fix this?](https://community.freefem.org/t/how-to-fix-this/2327)
**Author:** [@cfdyuewu](https://community.freefem.org/u/cfdyuewu)\ **Replies:** 2\ **Last updated:** [March 13, 2023, 1:56pm UTC](https://community.freefem.org/t/how-to-fix-this/2327 "2023-03-13T13:56:45Z")
when I run this code, it says that Assertion fail : (th == &fe\[1\]-\>Vh-\>Th) line :4386, in file lgfem.cpp Assertion fail : (th == &fe\[1\]-\>Vh-\>Th) line :4386, in file lgfem.cpp err code 6 , mpirank 0 ter… --- ## [Newton iteration of one-dimensional discontinuous galerkin finite element implicit scheme](https://community.freefem.org/t/newton-iteration-of-one-dimensional-discontinuous-galerkin-finite-element-implicit-scheme/2324)
**Author:** [@Qianrui](https://community.freefem.org/u/Qianrui)\ **Replies:** 1\ **Last updated:** [March 12, 2023, 7:22pm UTC](https://community.freefem.org/t/newton-iteration-of-one-dimensional-discontinuous-galerkin-finite-element-implicit-scheme/2324 "2023-03-12T19:22:51Z")
Can freefem++be used to calculate discontinuous finite element implicit schemes? Is it through Newton iteration? Does Freefrem++have built-in Newton iteration? --- ## [How to set the initial value on the boundary?](https://community.freefem.org/t/how-to-set-the-initial-value-on-the-boundary/2326)
**Author:** [@cfdyuewu](https://community.freefem.org/u/cfdyuewu)\ **Replies:** 0\ **Last updated:** [March 12, 2023, 3:37pm UTC](https://community.freefem.org/t/how-to-set-the-initial-value-on-the-boundary/2326 "2023-03-12T15:37:38Z")
I’m working on the example “large fluid problem” by using fem and newton iteration method, I want to set the value of Ux on b6 be 3, because newton method need to solve the incremental value, so I can’t directly assign t… --- ## [Problem with Neumann boundary conditions for discontinuous Galerkin method](https://community.freefem.org/t/problem-with-neumann-boundary-conditions-for-discontinuous-galerkin-method/2325)
**Author:** [@prabir.barman](https://community.freefem.org/u/prabir.barman)\ **Replies:** 0\ **Last updated:** [March 12, 2023, 1:43pm UTC](https://community.freefem.org/t/problem-with-neumann-boundary-conditions-for-discontinuous-galerkin-method/2325 "2023-03-12T13:43:20Z")
I am trying to impose flux boundary conditions (Neumann type) in the 2D heat conduction equation. The int1d(Th,3)(…) works fine for the Galerkin method, but this integration does not affect boundary values in discontinuo… --- ## [How to Access Appropriate Triangles in the Mesh](https://community.freefem.org/t/how-to-access-appropriate-triangles-in-the-mesh/1553)
**Author:** [@mariancantal](https://community.freefem.org/u/mariancantal)\ **Replies:** 2\ **Last updated:** [March 10, 2023, 8:05pm UTC](https://community.freefem.org/t/how-to-access-appropriate-triangles-in-the-mesh/1553 "2023-03-10T20:05:43Z")
Hi everyone! I am not sure if I am implementing the correct code for this problem: For my case, denote g1=\\gamma, gdiv =\\gamma. The domain \\Omega lies inside the rectangular domain O, where \\Gamma:=\\partial\\Omega.… --- ## [Graphics problem when connecting remotely (ssh + X11 forwarding) from a Mac](https://community.freefem.org/t/graphics-problem-when-connecting-remotely-ssh-x11-forwarding-from-a-mac/2320)
**Author:** [@etj](https://community.freefem.org/u/etj)\ **Replies:** 4\ **Last updated:** [March 10, 2023, 4:14pm UTC](https://community.freefem.org/t/graphics-problem-when-connecting-remotely-ssh-x11-forwarding-from-a-mac/2320 "2023-03-10T16:14:42Z")
Hello, I use FreeFem++ on several computers, connecting remotely with ssh and X11 forwarding. One of the computers has an old version: – FreeFem++ v 3.380000 (date Mer 24 jui 2015 20:46:58 CEST) On that computer, eve… --- ## [Mesh adaptation](https://community.freefem.org/t/mesh-adaptation/2319)
**Author:** [@Aud](https://community.freefem.org/u/Aud)\ **Replies:** 2\ **Last updated:** [March 10, 2023, 10:06am UTC](https://community.freefem.org/t/mesh-adaptation/2319 "2023-03-10T10:06:45Z")
Dear community, I would kindly like to have more explanation about the “adaptmesh” function in Freefem. The Freefem documentation is not so explicit for me. Thank you in advance. --- ## [Efficient solver and preconditionner for 3D Stokes Problem](https://community.freefem.org/t/efficient-solver-and-preconditionner-for-3d-stokes-problem/2318)
**Author:** [@Loic](https://community.freefem.org/u/Loic)\ **Replies:** 39\ **Last updated:** [March 9, 2023, 6:52am UTC](https://community.freefem.org/t/efficient-solver-and-preconditionner-for-3d-stokes-problem/2318 "2023-03-09T06:52:13Z")
Dear all, I am solving a 3D Stokes problem with PETSc in parallel, with this variationnal formulation grad(u)' \* grad(v) + grad(uB)' \* grad(vB) + grad(uC)' \* grad(vC) - div(u) \* q - div(v) \* p + epsq \* p \* q To solve … --- ## [Include two different PDE problems in PETSc](https://community.freefem.org/t/include-two-different-pde-problems-in-petsc/2265)
**Author:** [@Keita](https://community.freefem.org/u/Keita)\ **Replies:** 17\ **Last updated:** [March 9, 2023, 2:18am UTC](https://community.freefem.org/t/include-two-different-pde-problems-in-petsc/2265 "2023-03-09T02:18:49Z")
Hi FreeFem++ developers! Thank you very much for makingFF. I’d like to perform the 3D topology optimization, where the 3D elasticity problem and reaction-diffusion equation (RDE) are included, using PETSc. I am now at… --- ## [How to load .vtu files?](https://community.freefem.org/t/how-to-load-vtu-files/2131)
**Author:** [@fraphel](https://community.freefem.org/u/fraphel)\ **Replies:** 5\ **Last updated:** [March 7, 2023, 4:06am UTC](https://community.freefem.org/t/how-to-load-vtu-files/2131 "2023-03-07T04:06:53Z")
Hello, Is there a way to load .vtu files (generated by savevtk function)? It seems that this function is not implemented. If not, is there a way to read these files to get the mesh and the problem solution? Thanks a l… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=33) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=35)