# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=12 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 13 --- ## [Stokes Discontinous Galerkin](https://community.freefem.org/t/stokes-discontinous-galerkin/3696)
**Author:** [@Manel](https://community.freefem.org/u/Manel)\ **Replies:** 4\ **Last updated:** [January 21, 2025, 8:45pm UTC](https://community.freefem.org/t/stokes-discontinous-galerkin/3696 "2025-01-21T20:45:53Z")
Dear all, I implemented a discontinous Galerkin scheme to solve the stokes equations. The case P2dc-P1dc for velocity-pressure is good but the case P1dc-P0 does not work and I do not why. Does anyone have an idea what … --- ## [Developing region plane Poiseuille Flow: problem Inlet BC](https://community.freefem.org/t/developing-region-plane-poiseuille-flow-problem-inlet-bc/3697)
**Author:** [@lparras](https://community.freefem.org/u/lparras)\ **Replies:** 1\ **Last updated:** [January 21, 2025, 1:11pm UTC](https://community.freefem.org/t/developing-region-plane-poiseuille-flow-problem-inlet-bc/3697 "2025-01-21T13:11:35Z")
Dear all. I have developed a 2D flow to solve the steady NS equations for a more complicated mesh. Once I got the code working, I have tried to test it against some analytic problem. I have used the developing region of… --- ## [Is there any code on simulating fish-like locomotion](https://community.freefem.org/t/is-there-any-code-on-simulating-fish-like-locomotion/3699)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 0\ **Last updated:** [January 21, 2025, 11:44am UTC](https://community.freefem.org/t/is-there-any-code-on-simulating-fish-like-locomotion/3699 "2025-01-21T11:44:39Z")
Dear all, Has anyone simulated the locomotion of fish in water before using FreeFem++? --- ## [Several problem with complex number](https://community.freefem.org/t/several-problem-with-complex-number/3691)
**Author:** [@zezi-yang](https://community.freefem.org/u/zezi-yang)\ **Replies:** 6\ **Last updated:** [January 17, 2025, 7:53am UTC](https://community.freefem.org/t/several-problem-with-complex-number/3691 "2025-01-17T07:53:18Z")
Hello everyone, I have encountered several problems in the computing of complex numbers. The definition of inner product in my question is as follows. My question is whether my program needs to add conjugate when us… --- ## [PETSc integration of the non linear schrodinger equation](https://community.freefem.org/t/petsc-integration-of-the-non-linear-schrodinger-equation/3693)
**Author:** [@Alexei](https://community.freefem.org/u/Alexei)\ **Replies:** 1\ **Last updated:** [January 14, 2025, 12:22pm UTC](https://community.freefem.org/t/petsc-integration-of-the-non-linear-schrodinger-equation/3693 "2025-01-14T12:22:14Z")
Hoping that it can be helpful, I attach a code for parallel integration of the non-linear Schrodinger equation in a circular domain using PETSc/SLEPc. fiber-circle-time-SLEPc.edp (9.0 KB) The code uses an implicit midp… --- ## [UMFPACK WARNING singular matrix](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685)
**Author:** [@bchen-00](https://community.freefem.org/u/bchen-00)\ **Replies:** 4\ **Last updated:** [January 14, 2025, 6:18am UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685 "2025-01-14T06:18:25Z")
Hello, I have compiled the FreeFEM++ code successfully using the source code on main branch, but cannot use it to solve any problem (even the ones in example) without encountering " UMFPACK WARNING singular matrix " T… --- ## [How to mesh an interior rectangle?](https://community.freefem.org/t/how-to-mesh-an-interior-rectangle/3687)
**Author:** [@dxdydelight](https://community.freefem.org/u/dxdydelight)\ **Replies:** 1\ **Last updated:** [January 12, 2025, 5:03pm UTC](https://community.freefem.org/t/how-to-mesh-an-interior-rectangle/3687 "2025-01-12T17:03:40Z")
The overal boundary C I made with 4 lines. The line which separates B (a different material) from the rest of the interior I made with a single line - is this the correct approach ? i’m stuck on how to create A. If i s… --- ## [How to solve 2D fractional diffusion equation with convex domain in freeFeem?](https://community.freefem.org/t/how-to-solve-2d-fractional-diffusion-equation-with-convex-domain-in-freefeem/3688)
**Author:** [@kasim-Rabayo](https://community.freefem.org/u/kasim-Rabayo)\ **Replies:** 5\ **Last updated:** [January 12, 2025, 4:10pm UTC](https://community.freefem.org/t/how-to-solve-2d-fractional-diffusion-equation-with-convex-domain-in-freefeem/3688 "2025-01-12T16:10:24Z")
Hi-I need know how to solve 2D fractional diffusion equation with convex domain in Freefem. --- ## [I can't get .vtk file using PETCS](https://community.freefem.org/t/i-cant-get-vtk-file-using-petcs/3678)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 4\ **Last updated:** [January 10, 2025, 3:56pm UTC](https://community.freefem.org/t/i-cant-get-vtk-file-using-petcs/3678 "2025-01-10T15:56:29Z")
Dear all, I have a problem, I can’t get .vtk file when I use using parallel code with PETCS. The attached is the code. Can anyone explain why. Thank you in advance. Xuan ex2-overlapping\_mesh.edp (330 Bytes) --- ## [PETSc crashes for more than one process](https://community.freefem.org/t/petsc-crashes-for-more-than-one-process/3679)
**Author:** [@Alexei](https://community.freefem.org/u/Alexei)\ **Replies:** 2\ **Last updated:** [January 10, 2025, 2:14pm UTC](https://community.freefem.org/t/petsc-crashes-for-more-than-one-process/3679 "2025-01-10T14:14:35Z")
Hello, I have run into unexpected trouble with the following SLEPc code : fiber-SLEPc.edp (4.5 KB) which is a modification of the eigenvalue problems : schrodinger-harmonic-oscillator-1d-SLEPc.edp schrodinger-harmon… --- ## [Electrostatic stripline analysis segfaults during adaptation](https://community.freefem.org/t/electrostatic-stripline-analysis-segfaults-during-adaptation/3683)
**Author:** [@dxdydelight](https://community.freefem.org/u/dxdydelight)\ **Replies:** 0\ **Last updated:** [January 10, 2025, 6:10am UTC](https://community.freefem.org/t/electrostatic-stripline-analysis-segfaults-during-adaptation/3683 "2025-01-10T06:10:06Z")
Sorry for the large blob of text, but as a new user I cannot upload attachments. The code which has been included calculates the impedance of stripline electrostatically. It is a conversion of this , VERY old code, whi… --- ## [Can't read mesh on Windows CMD terminal](https://community.freefem.org/t/cant-read-mesh-on-windows-cmd-terminal/3680)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 1\ **Last updated:** [January 9, 2025, 11:36am UTC](https://community.freefem.org/t/cant-read-mesh-on-windows-cmd-terminal/3680 "2025-01-09T11:36:50Z")
Dear all, I meet a strange problem, that is I can’t read mesh on my Windows CMD terminal but I can on notepad++. Can anyone explain what’s wrong. --- ## [New finite element with dependence on neighbours](https://community.freefem.org/t/new-finite-element-with-dependence-on-neighbours/3653)
**Author:** [@fb77](https://community.freefem.org/u/fb77)\ **Replies:** 2\ **Last updated:** [January 9, 2025, 9:03am UTC](https://community.freefem.org/t/new-finite-element-with-dependence-on-neighbours/3653 "2025-01-09T09:03:35Z")
Hello to all experts, I am wondering if it is possible to define a new finite element type, where the interpolation points (as well as the base) depend not only on the current triangle, but also on the neighbours. This … --- ## [How to Handle Three-Dimensional Boundary Conditions](https://community.freefem.org/t/how-to-handle-three-dimensional-boundary-conditions/3664)
**Author:** [@raphael](https://community.freefem.org/u/raphael)\ **Replies:** 2\ **Last updated:** [January 9, 2025, 9:00am UTC](https://community.freefem.org/t/how-to-handle-three-dimensional-boundary-conditions/3664 "2025-01-09T09:00:03Z")
Hello guys, I am encountering some issues while trying to use the first-kind Nedelec elements. I am not sure how to apply the boundary conditions v×n=0 and ∇×u=0. I am unsure if setting the boundary degrees of freedom I… --- ## [Problem with 1D integral while using movemesh for Poisson Problem with Neumann Boundary Condition](https://community.freefem.org/t/problem-with-1d-integral-while-using-movemesh-for-poisson-problem-with-neumann-boundary-condition/3673)
**Author:** [@RaghunathBandha](https://community.freefem.org/u/RaghunathBandha)\ **Replies:** 5\ **Last updated:** [January 8, 2025, 12:29pm UTC](https://community.freefem.org/t/problem-with-1d-integral-while-using-movemesh-for-poisson-problem-with-neumann-boundary-condition/3673 "2025-01-08T12:29:43Z")
Hello, I have tried the Poisson problem with Neumann boundary. I am facing difficulty in the line 1D boundary integral under transformation. If du/dn=q given then qv ds is transformed to QV dS. If du/dn is not given the… --- ## [mpiBarrier(mpiCommWorld) not working correctly?](https://community.freefem.org/t/mpibarrier-mpicommworld-not-working-correctly/3676)
**Author:** [@Trueo](https://community.freefem.org/u/Trueo)\ **Replies:** 5\ **Last updated:** [January 8, 2025, 7:33am UTC](https://community.freefem.org/t/mpibarrier-mpicommworld-not-working-correctly/3676 "2025-01-08T07:33:58Z")
It seems like mpiBarrier(mpiCommWorld) is not functioning as expected. Here’s the situation: Given the following FreeFEM++ code: ///////////////////////////////////////////////////////////////////////// verbosity = 0; … --- ## [Stabilized FEM Method](https://community.freefem.org/t/stabilized-fem-method/3675)
**Author:** [@juanpaca](https://community.freefem.org/u/juanpaca)\ **Replies:** 4\ **Last updated:** [January 6, 2025, 6:50pm UTC](https://community.freefem.org/t/stabilized-fem-method/3675 "2025-01-06T18:50:30Z")
Hello everyone, I’m new in FreeFem and i’m trying to implement a stabilized FEM method, in particular i have the following linear form: My problem is in that summation over the triangles of the triangularization of t… --- ## [How to run parallel file in natepad++](https://community.freefem.org/t/how-to-run-parallel-file-in-natepad/3668)
**Author:** [@zxss](https://community.freefem.org/u/zxss)\ **Replies:** 1\ **Last updated:** [January 4, 2025, 6:40am UTC](https://community.freefem.org/t/how-to-run-parallel-file-in-natepad/3668 "2025-01-04T06:40:46Z")
Dear all, I have a question, can I directly run parallel file on my editor Notepad++ instead of using mpiexec command on my CMD terminal. Since I can directly run sequential file on Notepad++. But for parallel file, i… --- ## [Problem in boundary condition implementation while using mesh formed by movemesh](https://community.freefem.org/t/problem-in-boundary-condition-implementation-while-using-mesh-formed-by-movemesh/3666)
**Author:** [@RaghunathBandha](https://community.freefem.org/u/RaghunathBandha)\ **Replies:** 2\ **Last updated:** [January 3, 2025, 4:11pm UTC](https://community.freefem.org/t/problem-in-boundary-condition-implementation-while-using-mesh-formed-by-movemesh/3666 "2025-01-03T16:11:16Z")
Hello! I have solved the Poisson problem with Dirichlet boundary condition for an ellipse domain. I transformed the ellipse into a circle solved the problem in circle then got the solution in ellipse by inverse transfor… --- ## [Issues with warning when setting initial value](https://community.freefem.org/t/issues-with-warning-when-setting-initial-value/3670)
**Author:** [@zezi-yang](https://community.freefem.org/u/zezi-yang)\ **Replies:** 3\ **Last updated:** [January 3, 2025, 2:56pm UTC](https://community.freefem.org/t/issues-with-warning-when-setting-initial-value/3670 "2025-01-03T14:56:41Z")
Hello Everyone, I am currently working on Ginzburg-Landau equation using FreeFem, and I am facing difficulties in setting up initial value. I choose the exact solution as initial value, and when I try to use FreeFem … --- ## [Getting problem to write the integral term in FreeFem++ of Oldroyd Model of Order One](https://community.freefem.org/t/getting-problem-to-write-the-integral-term-in-freefem-of-oldroyd-model-of-order-one/3669)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [January 2, 2025, 4:22pm UTC](https://community.freefem.org/t/getting-problem-to-write-the-integral-term-in-freefem-of-oldroyd-model-of-order-one/3669 "2025-01-02T16:22:38Z")
Hello, all experts and respected professors I am trying to solve DG of Oldroyd Model of Order One with Backward Euler scheme in time. I am getting problem to write the integral term in FreeFem++. Here, is the equa… --- ## [Poisson Equation (Parallel Implementation)](https://community.freefem.org/t/poisson-equation-parallel-implementation/3665)
**Author:** [@salvo.giordano](https://community.freefem.org/u/salvo.giordano)\ **Replies:** 4\ **Last updated:** [December 30, 2024, 5:18pm UTC](https://community.freefem.org/t/poisson-equation-parallel-implementation/3665 "2024-12-30T17:18:18Z")
Hello, I am new to parallel implementation with FreeFem++, so I started by implementing a Poisson problem using domain decomposition, based on some examples I found online. I first implemented this code in a serial forma… --- ## [Regarding Error Indicator in FF++](https://community.freefem.org/t/regarding-error-indicator-in-ff/3661)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 7\ **Last updated:** [December 28, 2024, 6:12pm UTC](https://community.freefem.org/t/regarding-error-indicator-in-ff/3661 "2024-12-28T18:12:23Z")
Hello, all expert I am trying to write the following error indicator in FF++. Its FF++ code( according to me): Blockquote sqrt(int1d(Th)(hTriangle\*((dx(phi))^2+(dy(phi))^2))+intalledges(Th)((lenEdge\*((jump(dx(phi… --- ## [Problem in implementation of DG code for Stokes-Darcy interface problem](https://community.freefem.org/t/problem-in-implementation-of-dg-code-for-stokes-darcy-interface-problem/3616)
**Author:** [@Sweta](https://community.freefem.org/u/Sweta)\ **Replies:** 7\ **Last updated:** [December 27, 2024, 11:27am UTC](https://community.freefem.org/t/problem-in-implementation-of-dg-code-for-stokes-darcy-interface-problem/3616 "2024-12-27T11:27:42Z")
Dear all, I have implemented standard finite element code for coupled Stokes-Darcy problem (Here I am attaching the link of the pdf where the model problem has been described \[https://drive.google.com/drive/folders/1yj… --- ## [I am facing a problem to handel non-linearity in FreeFem++](https://community.freefem.org/t/i-am-facing-a-problem-to-handel-non-linearity-in-freefem/3654)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 7\ **Last updated:** [December 20, 2024, 3:55pm UTC](https://community.freefem.org/t/i-am-facing-a-problem-to-handel-non-linearity-in-freefem/3654 "2024-12-20T15:55:57Z")
Hello all expert, I am trying to solve Navier-stokes equation using Backward Euler scheme. I am facing problem with the convection term. Here, is the weak formulation Here, F(u,p) has u koronecker u which w… --- ## [Issues with Implementing a Nonlinear Boundary Condition in FreeFem](https://community.freefem.org/t/issues-with-implementing-a-nonlinear-boundary-condition-in-freefem/3648)
**Author:** [@romie090](https://community.freefem.org/u/romie090)\ **Replies:** 1\ **Last updated:** [December 19, 2024, 8:55am UTC](https://community.freefem.org/t/issues-with-implementing-a-nonlinear-boundary-condition-in-freefem/3648 "2024-12-19T08:55:03Z")
Hello Everyone, I am currently working on a simulation using FreeFem, and I am facing difficulties in implementing a nonlinear boundary condition for a PDE I am solving. Specifically, I am trying to impose a boundary co… --- ## [Generalized eigenvalue problem solving with Lagrange multipliers with EPSSOLVE](https://community.freefem.org/t/generalized-eigenvalue-problem-solving-with-lagrange-multipliers-with-epssolve/3650)
**Author:** [@alberic](https://community.freefem.org/u/alberic)\ **Replies:** 2\ **Last updated:** [December 19, 2024, 11:43am UTC](https://community.freefem.org/t/generalized-eigenvalue-problem-solving-with-lagrange-multipliers-with-epssolve/3650 "2024-12-19T11:43:50Z")
Hello, I am facing a problem with a generalized eigenvalues problem using EPSSolve in FreeFEM. I want to solve a variational formulation with constraints, which I handle using Lagrange multipliers. This leads to a matr… --- ## [Singular matrix in PETSc](https://community.freefem.org/t/singular-matrix-in-petsc/3644)
**Author:** [@abdobenf](https://community.freefem.org/u/abdobenf)\ **Replies:** 5\ **Last updated:** [December 18, 2024, 6:00pm UTC](https://community.freefem.org/t/singular-matrix-in-petsc/3644 "2024-12-18T18:00:37Z")
Hello, can anyone help find out where is the problem here. See the code below : matrix AA = \[\[A,B\], \[C,D\]\]; //Mat DD = AA; //set(DD, sparams = "-pc\_type lu -pc\_factor\_mat\_solver\_type mumps -mat\_mumps\_ic… --- ## [Composite spaces, on() and tgv=-1](https://community.freefem.org/t/composite-spaces-on-and-tgv-1/3579)
**Author:** [@fb77](https://community.freefem.org/u/fb77)\ **Replies:** 3\ **Last updated:** [December 18, 2024, 7:28am UTC](https://community.freefem.org/t/composite-spaces-on-and-tgv-1/3579 "2024-12-18T07:28:58Z")
It seems that there is a bug on composite spaces when using them with Dirichlet BC set with on() and tgv=-1. In the example of “Stokes with P2-iso-P1 elements” given in the documentation, setting tgv=-1 gives a wrong re… --- ## [Getting Problem to compute Intermediate velocity of Chan-Hilliard-Navier-stokes equation](https://community.freefem.org/t/getting-problem-to-compute-intermediate-velocity-of-chan-hilliard-navier-stokes-equation/3646)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [December 18, 2024, 5:52am UTC](https://community.freefem.org/t/getting-problem-to-compute-intermediate-velocity-of-chan-hilliard-navier-stokes-equation/3646 "2024-12-18T05:52:02Z")
Dear All, i am trying to solve Chan-Hilliard-Navier-Stokes equation by Discontinuous Galerkin Pressure Correction method. For that i have to compute an intermediate velocity vtilde. I am getting problem to solve the equa… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=11) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=13)