# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=16 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 17 --- ## [Newtons methods for unsteady problem](https://community.freefem.org/t/newtons-methods-for-unsteady-problem/1873)
**Author:** [@DongweiYe](https://community.freefem.org/u/DongweiYe)\ **Replies:** 12\ **Last updated:** [August 31, 2024, 2:30pm UTC](https://community.freefem.org/t/newtons-methods-for-unsteady-problem/1873 "2024-08-31T14:30:19Z")
Hi everyone, I meet a problem with implementing the unsteady NS equation with Newton method. I need to implement a periodical boundary condition on the inlet. However it seems that with Newton method, the convergence is… --- ## [Interpolation and prolongation/restriction](https://community.freefem.org/t/interpolation-and-prolongation-restriction/3459)
**Author:** [@etj](https://community.freefem.org/u/etj)\ **Replies:** 2\ **Last updated:** [August 30, 2024, 7:13pm UTC](https://community.freefem.org/t/interpolation-and-prolongation-restriction/3459 "2024-08-30T19:13:36Z")
Hello, Is is possible to do both (1) interpolation to/from a boundary and (2) restriction/prolongation between FE spaces with different numbers of components? For example, switch between \[P2,P1\] on Th and \[P2\] on a boun… --- ## [What objects can be pass through the mmap-semaphore plugin?](https://community.freefem.org/t/what-objects-can-be-pass-through-the-mmap-semaphore-plugin/3441)
**Author:** [@suavesito](https://community.freefem.org/u/suavesito)\ **Replies:** 1\ **Last updated:** [August 29, 2024, 7:56pm UTC](https://community.freefem.org/t/what-objects-can-be-pass-through-the-mmap-semaphore-plugin/3441 "2024-08-29T19:56:15Z")
Hi! I’m working to develop a Julia library to connect to FreeFEM++ using the mmap-semaphore plugin. The objective is to be able to pass vectors, meshes and solutions directly through mmap, without writing them to disk, … --- ## [Is it possible to access values of a P1 element at the nodes?](https://community.freefem.org/t/is-it-possible-to-access-values-of-a-p1-element-at-the-nodes/51)
**Author:** [@Neutrino](https://community.freefem.org/u/Neutrino)\ **Replies:** 11\ **Last updated:** [August 29, 2024, 6:00am UTC](https://community.freefem.org/t/is-it-possible-to-access-values-of-a-p1-element-at-the-nodes/51 "2024-08-29T06:00:33Z")
Hi there! Is it possible to access values of a P1 function at the nodes and put them in an array? Thank you. --- ## [Old example of Newton3D Using Boussinesq hypothesis gives seg-fault](https://community.freefem.org/t/old-example-of-newton3d-using-boussinesq-hypothesis-gives-seg-fault/3457)
**Author:** [@isharma25](https://community.freefem.org/u/isharma25)\ **Replies:** 6\ **Last updated:** [August 28, 2024, 3:21pm UTC](https://community.freefem.org/t/old-example-of-newton3d-using-boussinesq-hypothesis-gives-seg-fault/3457 "2024-08-28T15:21:48Z")
Hello, The example code from: FreeFem++ users | Main \>\> Newton3D is giving a seg-fault in the while loop, specifically the int3d(Th) functions are not working properly. I would like to solve this, any pointers would be… --- ## [Code sometimes does not store .vtu file](https://community.freefem.org/t/code-sometimes-does-not-store-vtu-file/3456)
**Author:** [@Alice](https://community.freefem.org/u/Alice)\ **Replies:** 2\ **Last updated:** [August 27, 2024, 11:21am UTC](https://community.freefem.org/t/code-sometimes-does-not-store-vtu-file/3456 "2024-08-27T11:21:04Z")
Hi All, I am trying to store .vtu file in my code. However there is a peculiar problem. It sometimes store vtu file sometimes not. Is there any reason? --- ## [How to get the symmetric tensor solution](https://community.freefem.org/t/how-to-get-the-symmetric-tensor-solution/3455)
**Author:** [@June](https://community.freefem.org/u/June)\ **Replies:** 1\ **Last updated:** [August 27, 2024, 9:46am UTC](https://community.freefem.org/t/how-to-get-the-symmetric-tensor-solution/3455 "2024-08-27T09:46:26Z")
Hello All, Most examples in FreeFEM Documentation are related to the model whose solution is fespace function or fespace vector function. Where can I find the example codes for the fespace symmetric tensor? --- ## [How to use gnuplot for Freefem on Windows](https://community.freefem.org/t/how-to-use-gnuplot-for-freefem-on-windows/3449)
**Author:** [@Alice](https://community.freefem.org/u/Alice)\ **Replies:** 4\ **Last updated:** [August 23, 2024, 12:19pm UTC](https://community.freefem.org/t/how-to-use-gnuplot-for-freefem-on-windows/3449 "2024-08-23T12:19:33Z")
Hi All I am trying to plot on freefem by using gnuplot. I tried this example Visualization. But the plot did not come from Gnuplot . I want to get this .Can anyone help? --- ## [How to avoid a null solution for the Helmholtz PDE with Dirichlet BC?](https://community.freefem.org/t/how-to-avoid-a-null-solution-for-the-helmholtz-pde-with-dirichlet-bc/3451)
**Author:** [@Songtech-0912](https://community.freefem.org/u/Songtech-0912)\ **Replies:** 5\ **Last updated:** [August 23, 2024, 8:19am UTC](https://community.freefem.org/t/how-to-avoid-a-null-solution-for-the-helmholtz-pde-with-dirichlet-bc/3451 "2024-08-23T08:19:41Z")
Hi all! I am a beginner to freefem, please excuse any gaps in my knowledge. So as part of my research I am doing numerical simulations of the (vector) Helmholz equation in the time domain: -\\nabla^2 \\mathbf{E} - k^2 \\m… --- ## [Stability problem related to SUPG](https://community.freefem.org/t/stability-problem-related-to-supg/3382)
**Author:** [@Walid](https://community.freefem.org/u/Walid)\ **Replies:** 22\ **Last updated:** [August 19, 2024, 6:01pm UTC](https://community.freefem.org/t/stability-problem-related-to-supg/3382 "2024-08-19T18:01:43Z")
Hello All, I hope you are fine. I am trying to solve 4 coupled PDE as below ∇.∇V=−q(Np-Ne-Nn)/ϵ ∂Ne/∂t +∇⋅(Ne.(-We)-De.∇Ne) = Se ∂Np/∂t +∇⋅(Np.(Wp)-Dp.∇Np) = Sp ∂Nn/∂t +∇⋅(Nn.(-Wn)-Dn.∇Nn) = Sn I have tried to … --- ## [How to handle advection-term involving two unknows?](https://community.freefem.org/t/how-to-handle-advection-term-involving-two-unknows/3411)
**Author:** [@Hemanta822](https://community.freefem.org/u/Hemanta822)\ **Replies:** 2\ **Last updated:** [August 19, 2024, 5:56pm UTC](https://community.freefem.org/t/how-to-handle-advection-term-involving-two-unknows/3411 "2024-08-19T17:56:11Z")
Hello All, I am trying to implement a temperature equation in the fluid system. I have a term (u \\dot \\nabla T) that couples velocity and temperature in the temperature equation. How can I handle such a term? Any help o… --- ## [How to use Tetgen to generate meshes for coaxial cylinders?](https://community.freefem.org/t/how-to-use-tetgen-to-generate-meshes-for-coaxial-cylinders/3447)
**Author:** [@qingYang](https://community.freefem.org/u/qingYang)\ **Replies:** 2\ **Last updated:** [August 17, 2024, 9:59am UTC](https://community.freefem.org/t/how-to-use-tetgen-to-generate-meshes-for-coaxial-cylinders/3447 "2024-08-17T09:59:56Z")
Dear Freefem users: I recently encountered a problem where I encountered the following error when using Tetgen to generate tetrahedral meshes for three coaxial cylinders. erro message : \[Assertion fail : (tabregion.N( … --- ## [Streamlines when re=1000](https://community.freefem.org/t/streamlines-when-re-1000/3438)
**Author:** [@Alice](https://community.freefem.org/u/Alice)\ **Replies:** 6\ **Last updated:** [August 15, 2024, 11:21am UTC](https://community.freefem.org/t/streamlines-when-re-1000/3438 "2024-08-15T11:21:15Z")
Hi All, I am trying to plot streamlines for re=1000. I need to show the lines near corners but when I try to show my image looks too intense on the center like this: but my aim is to show it like this . How can I … --- ## [Gradient descent for heat equation](https://community.freefem.org/t/gradient-descent-for-heat-equation/3443)
**Author:** [@Sami](https://community.freefem.org/u/Sami)\ **Replies:** 0\ **Last updated:** [August 14, 2024, 2:23pm UTC](https://community.freefem.org/t/gradient-descent-for-heat-equation/3443 "2024-08-14T14:23:29Z")
Hello, I’m a beginner in FreeFem++ I am trying to solve the heat equation but solution of the heat equation is not converging to the solution of the gradient descent. Additionally the gradient of the objective function… --- ## [Problem with 3d incompressible NS equation](https://community.freefem.org/t/problem-with-3d-incompressible-ns-equation/3434)
**Author:** [@localhost](https://community.freefem.org/u/localhost)\ **Replies:** 3\ **Last updated:** [August 13, 2024, 5:56am UTC](https://community.freefem.org/t/problem-with-3d-incompressible-ns-equation/3434 "2024-08-13T05:56:56Z")
Hello, I am trying to write Freefem++ code for the unsteady Navier Stokes equations in 3D using Newton’s method. I found a similar example in the FreeFem hpddm examples. I changed it into 3d version. The problem is whe… --- ## [How mixed condition deal in fem through free fem coding](https://community.freefem.org/t/how-mixed-condition-deal-in-fem-through-free-fem-coding/521)
**Author:** [@Shah](https://community.freefem.org/u/Shah)\ **Replies:** 1\ **Last updated:** [August 12, 2024, 10:16pm UTC](https://community.freefem.org/t/how-mixed-condition-deal-in-fem-through-free-fem-coding/521 "2024-08-12T22:16:43Z")
How free fem coding working for mixed and Neumann condition? --- ## [Check for positive semi-definiteness](https://community.freefem.org/t/check-for-positive-semi-definiteness/3426)
**Author:** [@jcvillaquira](https://community.freefem.org/u/jcvillaquira)\ **Replies:** 3\ **Last updated:** [August 12, 2024, 3:52pm UTC](https://community.freefem.org/t/check-for-positive-semi-definiteness/3426 "2024-08-12T15:52:30Z")
Hi, I need to verify if a matrix is positive (semi)-definite, ideally without computing the eigenvalues. Is there a standard way? Thanks in advance! --- ## [Trouble generating a mesh with high number of borders](https://community.freefem.org/t/trouble-generating-a-mesh-with-high-number-of-borders/3437)
**Author:** [@Pwaroquier](https://community.freefem.org/u/Pwaroquier)\ **Replies:** 1\ **Last updated:** [August 12, 2024, 10:04am UTC](https://community.freefem.org/t/trouble-generating-a-mesh-with-high-number-of-borders/3437 "2024-08-12T10:04:22Z")
Hello, I am generating meshes with FreeFEM that contain a huge number of borders. When I try with a few borders, it works, the mesh generates and I can plot it. However, when I increase the number of borders, the plot… --- ## [Inverse problems in freefem](https://community.freefem.org/t/inverse-problems-in-freefem/3436)
**Author:** [@VaishnaviGnanam](https://community.freefem.org/u/VaishnaviGnanam)\ **Replies:** 0\ **Last updated:** [August 12, 2024, 7:11am UTC](https://community.freefem.org/t/inverse-problems-in-freefem/3436 "2024-08-12T07:11:03Z")
I have been trying to solve a inverse problem in freefem++. while writing the variational formulation due to that inverse problem (since the unknown is converted in terms of solution) i am getting product of two integral… --- ## [Lid-driven cavity problem for MPFF code gives error for a modified NSEs model](https://community.freefem.org/t/lid-driven-cavity-problem-for-mpff-code-gives-error-for-a-modified-nses-model/3421)
**Author:** [@ozil101](https://community.freefem.org/u/ozil101)\ **Replies:** 1\ **Last updated:** [August 6, 2024, 3:10pm UTC](https://community.freefem.org/t/lid-driven-cavity-problem-for-mpff-code-gives-error-for-a-modified-nses-model/3421 "2024-08-06T15:10:16Z")
Hi, Dear respected Professors @fb77 @julienG , thank you for your kind guidance and help. I am struggling to fix this bug in my code, please help to make the code run smoothly. NSEs modified momentum model: error: … --- ## [Can I use FreeFem to calculate resonance modes?](https://community.freefem.org/t/can-i-use-freefem-to-calculate-resonance-modes/3420)
**Author:** [@simmania](https://community.freefem.org/u/simmania)\ **Replies:** 0\ **Last updated:** [August 1, 2024, 12:38pm UTC](https://community.freefem.org/t/can-i-use-freefem-to-calculate-resonance-modes/3420 "2024-08-01T12:38:32Z")
Hi all, I’m investigating if I can use FreeFem for my new project. For this project I would like to calculate the resonance frequencies (and modes) for different objects. This to be able to synthesize the sound it woul… --- ## [How do Simulation in FreeFem++ Cs or FreeFem v4.14 of Heat equation using random initial ata](https://community.freefem.org/t/how-do-simulation-in-freefem-cs-or-freefem-v4-14-of-heat-equation-using-random-initial-ata/3417)
**Author:** [@Monirul25](https://community.freefem.org/u/Monirul25)\ **Replies:** 0\ **Last updated:** [July 29, 2024, 9:05am UTC](https://community.freefem.org/t/how-do-simulation-in-freefem-cs-or-freefem-v4-14-of-heat-equation-using-random-initial-ata/3417 "2024-07-29T09:05:33Z")
Helo everyone, i want to what is the commnad in FreeFem++ to write random initial data so that i can plot the simulation results of the approximate solution in different time. Let me know please if any one know. Basicall… --- ## [Radiation using view factors](https://community.freefem.org/t/radiation-using-view-factors/3408)
**Author:** [@PierreAntonetti](https://community.freefem.org/u/PierreAntonetti)\ **Replies:** 1\ **Last updated:** [July 25, 2024, 9:25am UTC](https://community.freefem.org/t/radiation-using-view-factors/3408 "2024-07-25T09:25:28Z")
Hello, Does anybody already manage to implement the triangle thermal radiation test case using the numerical calculated view factors ? This example comes from Comsol : link Thank for helping --- ## [Streamlines using the Elmer method](https://community.freefem.org/t/streamlines-using-the-elmer-method/3407)
**Author:** [@PierreAntonetti](https://community.freefem.org/u/PierreAntonetti)\ **Replies:** 10\ **Last updated:** [July 25, 2024, 9:23am UTC](https://community.freefem.org/t/streamlines-using-the-elmer-method/3407 "2024-07-25T09:23:29Z")
Hello, I want to get the streamline function \\psi of a 2d incompressible field U=(u,v) cause the isoline of \\psi are the streamlines (orthogonal to U). I’ve seen two related topics on this forum mainly using the vortic… --- ## [Grounding system of electric power plant analysis](https://community.freefem.org/t/grounding-system-of-electric-power-plant-analysis/3412)
**Author:** [@duskot](https://community.freefem.org/u/duskot)\ **Replies:** 0\ **Last updated:** [July 25, 2024, 7:54am UTC](https://community.freefem.org/t/grounding-system-of-electric-power-plant-analysis/3412 "2024-07-25T07:54:25Z")
Dear, I would like to develop a model of the grounding system of the electric power plant. I need to analyze the electric field and current field in the ground of that plant. Please, let me know if it is possible to d… --- ## [Wrong orientation of "internal" boundary elements](https://community.freefem.org/t/wrong-orientation-of-internal-boundary-elements/3402)
**Author:** [@fb77](https://community.freefem.org/u/fb77)\ **Replies:** 0\ **Last updated:** [July 17, 2024, 4:28pm UTC](https://community.freefem.org/t/wrong-orientation-of-internal-boundary-elements/3402 "2024-07-17T16:28:06Z")
Hello, I am importing a simple 2d mesh from a file meshtest.msh as 10 9 11 0. 0. 1 0. 1. 10 1. 0. 1 2. 0. 4 0. 2. 10 1. 2. 2 2. 2. 4 2. 3. 4 1. 3. 4 0. 3. 10 1 3 2 11 3 4 6 11 3 6 2 11 4 7 6 11 6 5 2 99 8 6 7 11 10 5 6… --- ## [The saddle point system of the mixed finite element](https://community.freefem.org/t/the-saddle-point-system-of-the-mixed-finite-element/3400)
**Author:** [@mohamed](https://community.freefem.org/u/mohamed)\ **Replies:** 6\ **Last updated:** [July 17, 2024, 4:26am UTC](https://community.freefem.org/t/the-saddle-point-system-of-the-mixed-finite-element/3400 "2024-07-17T04:26:11Z")
hello there, I’m trying to get the underlying linear system of the mixed finite formulation of the poisson problem. The one of the form is there a way to do so in freefem. --- ## [Micropolar Fluid Flow Numerical Simulation: Modified NSEs in Lid-driven cavity flow problem](https://community.freefem.org/t/micropolar-fluid-flow-numerical-simulation-modified-nses-in-lid-driven-cavity-flow-problem/3332)
**Author:** [@ozil101](https://community.freefem.org/u/ozil101)\ **Replies:** 4\ **Last updated:** [July 16, 2024, 2:06pm UTC](https://community.freefem.org/t/micropolar-fluid-flow-numerical-simulation-modified-nses-in-lid-driven-cavity-flow-problem/3332 "2024-07-16T14:06:52Z")
Hi respected Professor, and thank you so much for your valuable and very kind guidances. I get some errors when I modified my original Lid-driven cavity flow code for mpff specific and modified version of NSEs as followi… --- ## [When the data is given but not the analytical solution, how to find out L2H1 error for heat equation](https://community.freefem.org/t/when-the-data-is-given-but-not-the-analytical-solution-how-to-find-out-l2h1-error-for-heat-equation/3397)
**Author:** [@Shrvs](https://community.freefem.org/u/Shrvs)\ **Replies:** 0\ **Last updated:** [July 15, 2024, 1:30pm UTC](https://community.freefem.org/t/when-the-data-is-given-but-not-the-analytical-solution-how-to-find-out-l2h1-error-for-heat-equation/3397 "2024-07-15T13:30:14Z")
To be precise after finding the reference solution with the given data on finer mesh (tau=1/2^9, h=1/80)and approximate solution on coarser mesh(spatial and time points are less(tau=1/2^4, h=1/10) in comparison with the … --- ## [Matrix/Array multiplication](https://community.freefem.org/t/matrix-array-multiplication/3394)
**Author:** [@HMasson](https://community.freefem.org/u/HMasson)\ **Replies:** 1\ **Last updated:** [July 12, 2024, 3:29pm UTC](https://community.freefem.org/t/matrix-array-multiplication/3394 "2024-07-12T15:29:27Z")
Hello, I am using a Gaussian quadrature method for computing statistical moments. I am running into a surprising issue, the following bit of code does not work : real\[int\] A = \[1, 2, 3\]; real\[int\] B = \[4, 5, 6\]; real\[… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=15) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=17)