# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=27 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 28 --- ## [Integral of a function and the projection of this function are not the same](https://community.freefem.org/t/integral-of-a-function-and-the-projection-of-this-function-are-not-the-same/2721)
**Author:** [@larismartins](https://community.freefem.org/u/larismartins)\ **Replies:** 9\ **Last updated:** [September 27, 2023, 11:35am UTC](https://community.freefem.org/t/integral-of-a-function-and-the-projection-of-this-function-are-not-the-same/2721 "2023-09-27T11:35:11Z")
Hi everyone! I’m trying to prove the following result but FreeFem++ is giving me different values for each DoF of the space P1(K). This is my code: load "qf11to25" //------------------Global Mesh------------------… --- ## [Parent map domain for FreeFem](https://community.freefem.org/t/parent-map-domain-for-freefem/2713)
**Author:** [@Erika](https://community.freefem.org/u/Erika)\ **Replies:** 3\ **Last updated:** [September 25, 2023, 10:48am UTC](https://community.freefem.org/t/parent-map-domain-for-freefem/2713 "2023-09-25T10:48:56Z")
Hi, I need to implement a definition where the map from parent to physical domain is required. How can I find the parent domain? There is anyone who has already implemented a map from parent to physical domain in FreeFe… --- ## [Plot of a FE function without the underlying mesh](https://community.freefem.org/t/plot-of-a-fe-function-without-the-underlying-mesh/2720)
**Author:** [@luca.liverotti](https://community.freefem.org/u/luca.liverotti)\ **Replies:** 3\ **Last updated:** [September 22, 2023, 9:47am UTC](https://community.freefem.org/t/plot-of-a-fe-function-without-the-underlying-mesh/2720 "2023-09-22T09:47:50Z")
Hi, I would like to plot a FE function without the background mesh (see attached image to see the background mesh). Is it possible? Thanks. prova.pdf (601.1 KB) --- ## [Domain Decomposition and fem variables](https://community.freefem.org/t/domain-decomposition-and-fem-variables/2711)
**Author:** [@llober](https://community.freefem.org/u/llober)\ **Replies:** 1\ **Last updated:** [September 21, 2023, 2:45pm UTC](https://community.freefem.org/t/domain-decomposition-and-fem-variables/2711 "2023-09-21T14:45:55Z")
In the example about Domain Decomposition, for the “Schwarz non overlapping Scheme”, lambda is actualized as: lambda = lambda - (u-U)/2 What I don’t really understand is that U is a fem variable defined inside a mostly … --- ## [Normal Derivative values at boundary](https://community.freefem.org/t/normal-derivative-values-at-boundary/1249)
**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\ **Replies:** 3\ **Last updated:** [September 21, 2023, 12:10pm UTC](https://community.freefem.org/t/normal-derivative-values-at-boundary/1249 "2023-09-21T12:10:29Z")
Dear All I am trying to get the normal derivative value at a specified boundary. for this I have written code as: real Nu = int1d(Th, hot)( dx(T)\*N.x + dy(T)\*N.y); for( int n1 = 0; n1\<=20 ; n1++) { court\<\< Nu(20/n… --- ## [Compute average value](https://community.freefem.org/t/compute-average-value/2166)
**Author:** [@larismartins](https://community.freefem.org/u/larismartins)\ **Replies:** 1\ **Last updated:** [September 21, 2023, 8:28am UTC](https://community.freefem.org/t/compute-average-value/2166 "2023-09-21T08:28:14Z")
Hi there, me again I know that freefem has a function to compute (4.28), but does it have one to compute the average value (4.29)? Couldn’t find anything in the documentation --- ## [How to compute length of a parametric curve by taking input from user in FREEFEM++?](https://community.freefem.org/t/how-to-compute-length-of-a-parametric-curve-by-taking-input-from-user-in-freefem/2714)
**Author:** [@RaghunathBandha](https://community.freefem.org/u/RaghunathBandha)\ **Replies:** 1\ **Last updated:** [September 19, 2023, 4:37pm UTC](https://community.freefem.org/t/how-to-compute-length-of-a-parametric-curve-by-taking-input-from-user-in-freefem/2714 "2023-09-19T16:37:46Z")
I want to compute length of parametric curve r(t)=\ where t in \[a,b\]. Please help me to write an FREEFEM code where user can give any parametric curve. I should able to compute the length. --- ## [Remove constant pressure solution using nullspace with PETSc](https://community.freefem.org/t/remove-constant-pressure-solution-using-nullspace-with-petsc/2712)
**Author:** [@cmd](https://community.freefem.org/u/cmd)\ **Replies:** 11\ **Last updated:** [September 18, 2023, 8:06pm UTC](https://community.freefem.org/t/remove-constant-pressure-solution-using-nullspace-with-petsc/2712 "2023-09-18T20:06:10Z")
When solving (Navier-)Stokes equations with BC (Dirichlet or Neumann) on the velocity only, the pressure is only defined up to an additive constant. There are examples in the FF documentation that use a penalization ter… --- ## [I put this homemade viewer, mjmdatascope, on github,](https://community.freefem.org/t/i-put-this-homemade-viewer-mjmdatascope-on-github/2707)
**Author:** [@marchywka](https://community.freefem.org/u/marchywka)\ **Replies:** 0\ **Last updated:** [September 14, 2023, 1:36pm UTC](https://community.freefem.org/t/i-put-this-homemade-viewer-mjmdatascope-on-github/2707 "2023-09-14T13:36:14Z")
On the one hand this is a big distraction but it is something I wanted to do before and AFAICT there is not a good way to look at 1D data in FF. I’ve been using this viewer for testing some code and also wrote an inte… --- ## [How to properly check that a Neumann/Robin boundary condition is satisfied](https://community.freefem.org/t/how-to-properly-check-that-a-neumann-robin-boundary-condition-is-satisfied/2705)
**Author:** [@jna1g18](https://community.freefem.org/u/jna1g18)\ **Replies:** 4\ **Last updated:** [September 14, 2023, 1:03pm UTC](https://community.freefem.org/t/how-to-properly-check-that-a-neumann-robin-boundary-condition-is-satisfied/2705 "2023-09-14T13:03:36Z")
Hi all, what is the proper way to check that a Neumann/Robin boundary condition is satisified at a boundary? For example, if I have \\nabla c\\cdot\\hat{n}=0 at a particular boundary and I insert this into the weak form of … --- ## [About high order Whitney-2 forms basis function](https://community.freefem.org/t/about-high-order-whitney-2-forms-basis-function/2706)
**Author:** [@deepdeepdark](https://community.freefem.org/u/deepdeepdark)\ **Replies:** 0\ **Last updated:** [September 14, 2023, 12:38pm UTC](https://community.freefem.org/t/about-high-order-whitney-2-forms-basis-function/2706 "2023-09-14T12:38:28Z")
Hello, everyone! I’m trying to finish a TDFEM program for electromagnetics. This is my reference paper: R. N. Rieben and D. A. White, “Verification of high-order mixed finite-element solution of transient magnetic diffu… --- ## [Implementing FreeFem on a problem including equation in the non weak form format](https://community.freefem.org/t/implementing-freefem-on-a-problem-including-equation-in-the-non-weak-form-format/2700)
**Author:** [@soniase](https://community.freefem.org/u/soniase)\ **Replies:** 13\ **Last updated:** [September 14, 2023, 11:28am UTC](https://community.freefem.org/t/implementing-freefem-on-a-problem-including-equation-in-the-non-weak-form-format/2700 "2023-09-14T11:28:28Z")
I have a system of partial differential equations (PDEs) that I’ve discretized in time using a specific scheme. Now, I want to discretize it in space using finite elements. However, I’m facing an issue: my last equation … --- ## [How to 1D integrate along a path inside mesh](https://community.freefem.org/t/how-to-1d-integrate-along-a-path-inside-mesh/700)
**Author:** [@amtravco](https://community.freefem.org/u/amtravco)\ **Replies:** 7\ **Last updated:** [September 14, 2023, 8:30am UTC](https://community.freefem.org/t/how-to-1d-integrate-along-a-path-inside-mesh/700 "2023-09-14T08:30:54Z")
Suppose I have a mesh Th defined in the square from x = 0 to 1, y = 0 to 1. I solve a PDE on this mesh, getting solution u. Now I want to know the line integral of u along the straight path from (0, 1/2) to (1, 1/2), tha… --- ## [How to determine the normal flux along a curved surface?](https://community.freefem.org/t/how-to-determine-the-normal-flux-along-a-curved-surface/756)
**Author:** [@Mr.Good](https://community.freefem.org/u/Mr.Good)\ **Replies:** 5\ **Last updated:** [September 13, 2023, 11:39am UTC](https://community.freefem.org/t/how-to-determine-the-normal-flux-along-a-curved-surface/756 "2023-09-13T11:39:57Z")
Dear users, I am working on a Natural convection problem via freeFEM? A researcher has plotted the results of Normal(grad(T)) along a circle see the top right figure. what will be the command of Normal(grad(T)) al… --- ## [Aspect ratio of adapted mesh](https://community.freefem.org/t/aspect-ratio-of-adapted-mesh/2703)
**Author:** [@jna1g18](https://community.freefem.org/u/jna1g18)\ **Replies:** 5\ **Last updated:** [September 13, 2023, 12:37pm UTC](https://community.freefem.org/t/aspect-ratio-of-adapted-mesh/2703 "2023-09-13T12:37:50Z")
Hi all, I have a question regarding the quality of my adapted mesh. The model I am solving has three unknowns (u1, u2 and phi), two of which (u1 and u2) exhibit boundary layers along two of the boundaries. At each timest… --- ## [Zero-flux boundary condition](https://community.freefem.org/t/zero-flux-boundary-condition/2699)
**Author:** [@jna1g18](https://community.freefem.org/u/jna1g18)\ **Replies:** 15\ **Last updated:** [September 13, 2023, 11:45am UTC](https://community.freefem.org/t/zero-flux-boundary-condition/2699 "2023-09-13T11:45:46Z")
Hi all, I have a question regarding a zero flux boundary condition in my model. First, I’ll input the model equations and the relevant boundary conditions, as well as the domain: Equations: \\frac{\\partial c\_1}{\\part… --- ## [Suppress "-options\_left" when using PETSc](https://community.freefem.org/t/suppress-options-left-when-using-petsc/2702)
**Author:** [@cmd](https://community.freefem.org/u/cmd)\ **Replies:** 1\ **Last updated:** [September 12, 2023, 4:58pm UTC](https://community.freefem.org/t/suppress-options-left-when-using-petsc/2702 "2023-09-12T16:58:20Z")
Hi all, It seems there may have been a change in the default verbosity when using PETSc in FreeFEM. Since updating my FF build, I’ve gotten a lot more output even with -v 0. Is there a way to force-suppress these new wa… --- ## [How to set boundary conditions where u multiplied by the boundary normal vector or u multiplied by the boundary tangent vector equals 0?](https://community.freefem.org/t/how-to-set-boundary-conditions-where-u-multiplied-by-the-boundary-normal-vector-or-u-multiplied-by-the-boundary-tangent-vector-equals-0/2698)
**Author:** [@Kingexitroot](https://community.freefem.org/u/Kingexitroot)\ **Replies:** 0\ **Last updated:** [September 11, 2023, 3:12am UTC](https://community.freefem.org/t/how-to-set-boundary-conditions-where-u-multiplied-by-the-boundary-normal-vector-or-u-multiplied-by-the-boundary-tangent-vector-equals-0/2698 "2023-09-11T03:12:21Z")
Hello everyone. I have the following question: u is a 2D vector, and I need to impose the boundary conditions un=0 or ut=0, where n and t are the boundary normal and tangential vectors, respectively. I couldn’t find the… --- ## [How to correctly define a mixed finite element system in FreeFEM?](https://community.freefem.org/t/how-to-correctly-define-a-mixed-finite-element-system-in-freefem/2696)
**Author:** [@Kingexitroot](https://community.freefem.org/u/Kingexitroot)\ **Replies:** 1\ **Last updated:** [September 11, 2023, 2:31am UTC](https://community.freefem.org/t/how-to-correctly-define-a-mixed-finite-element-system-in-freefem/2696 "2023-09-11T02:31:32Z")
Now I need to solve a system of equations using FreeFEM, and I’m not sure if the format of the equations I’ve defined is correct. In fact, I only know how to define and solve individual equations using FreeFEM, so I trie… --- ## [Solving Poisson's equation with Dirac delta function](https://community.freefem.org/t/solving-poissons-equation-with-dirac-delta-function/2036)
**Author:** [@StephenGPN](https://community.freefem.org/u/StephenGPN)\ **Replies:** 4\ **Last updated:** [September 10, 2023, 9:21pm UTC](https://community.freefem.org/t/solving-poissons-equation-with-dirac-delta-function/2036 "2023-09-10T21:21:03Z")
Hello everybody! I clearly understand how to solve a standard Poisson’s equation in FF++. But can anyone suggest me how to solve it having the Dirac delta function as a RHS? I’m pretty newbie with FF+ so I’d appreciate … --- ## [Movemesh with level set defined geometry](https://community.freefem.org/t/movemesh-with-level-set-defined-geometry/2693)
**Author:** [@gurkanceren](https://community.freefem.org/u/gurkanceren)\ **Replies:** 3\ **Last updated:** [September 10, 2023, 4:31pm UTC](https://community.freefem.org/t/movemesh-with-level-set-defined-geometry/2693 "2023-09-10T16:31:51Z")
Hello everyone, I have compiled the developer version of FreeFem to have my hands on mmg2d function and created the attached mesh where the flower like geometry is defined by a level set function as: A = x^2 + y^2; ls… --- ## [How to create mesh from levet set function](https://community.freefem.org/t/how-to-create-mesh-from-levet-set-function/2680)
**Author:** [@gurkanceren](https://community.freefem.org/u/gurkanceren)\ **Replies:** 53\ **Last updated:** [September 9, 2023, 7:36pm UTC](https://community.freefem.org/t/how-to-create-mesh-from-levet-set-function/2680 "2023-09-09T19:36:37Z")
Hello, I am a newbee in the platform and I want to create a square domain with a 3 petal flower-like shape in it (I have the level set definition of this flower geometry, shared below). Then I want to create a mesh in t… --- ## [Elasticity problem](https://community.freefem.org/t/elasticity-problem/2689)
**Author:** [@moufide](https://community.freefem.org/u/moufide)\ **Replies:** 11\ **Last updated:** [September 8, 2023, 9:13pm UTC](https://community.freefem.org/t/elasticity-problem/2689 "2023-09-08T21:13:42Z")
Bonjour cher Professeur Ma compilation affiche je n’ai pas compris – Square mesh : nb vertices =22 , nb triangles = 20 , nb boundary edges 22 – FESpace: Nb of Nodes 44 Nb of DoF 132 – Solve : min -1.3237e-12 max… --- ## [Edge mesh on FreeFem++](https://community.freefem.org/t/edge-mesh-on-freefem/2687)
**Author:** [@larismartins](https://community.freefem.org/u/larismartins)\ **Replies:** 13\ **Last updated:** [September 8, 2023, 3:13pm UTC](https://community.freefem.org/t/edge-mesh-on-freefem/2687 "2023-09-08T15:13:44Z")
Hi guys, is it possible to build a edge mesh on FreeFem++? For example, given a triangle, I wish to partition each edge in 2 and build a FEM space on each piece. --- ## [Numerical results error](https://community.freefem.org/t/numerical-results-error/2688)
**Author:** [@moufide](https://community.freefem.org/u/moufide)\ **Replies:** 8\ **Last updated:** [September 7, 2023, 6:36pm UTC](https://community.freefem.org/t/numerical-results-error/2688 "2023-09-07T18:36:58Z")
Hello everyone I modified the code of the elasticity equation in 3D to evaluate the evolution of energy as a function of time…but I don’t know why it does not reflect what I obtained theoretically. Normally when I put … --- ## [Modified Weak Galerkin Finite Element Method](https://community.freefem.org/t/modified-weak-galerkin-finite-element-method/2656)
**Author:** [@ahbabil1983](https://community.freefem.org/u/ahbabil1983)\ **Replies:** 10\ **Last updated:** [September 6, 2023, 2:28pm UTC](https://community.freefem.org/t/modified-weak-galerkin-finite-element-method/2656 "2023-09-06T14:28:55Z")
Hello everyone, I want to write a FreeFEM++ program about the Poisson Problem -∆u=f in Ω u=g on ∂Ω using the Modified Weak Galerkin Finite Element Method ∑\_T〈∇\_w u\_h,∇\_w v\_h 〉T + ∑\_e h^(-1) 〈\[\[u\_h \]\], \[\[v\_h \]\]〉e = 〈f… --- ## [Post-processing with P2b elements](https://community.freefem.org/t/post-processing-with-p2b-elements/2678)
**Author:** [@single\_way](https://community.freefem.org/u/single_way)\ **Replies:** 2\ **Last updated:** [September 6, 2023, 12:26pm UTC](https://community.freefem.org/t/post-processing-with-p2b-elements/2678 "2023-09-06T12:26:19Z")
Hello everyone! I am new to Freefem. I am using P2b elements in my simulation. I want to export the data and plot the field in another software. However, Matlab and Paraview do not support such type of element. Is ther… --- ## [How to include a function of independent variable x into weak form?](https://community.freefem.org/t/how-to-include-a-function-of-independent-variable-x-into-weak-form/2686)
**Author:** [@jna1g18](https://community.freefem.org/u/jna1g18)\ **Replies:** 0\ **Last updated:** [September 6, 2023, 12:06pm UTC](https://community.freefem.org/t/how-to-include-a-function-of-independent-variable-x-into-weak-form/2686 "2023-09-06T12:06:11Z")
Hi all, what’s the best way to include a function of spatial variable x into the weak form? I know that freefem has x and y built in, but is it still necessary to interpolate them onto the mesh or can I simply enter them… --- ## [1D discontinuous Galerkin FEM code](https://community.freefem.org/t/1d-discontinuous-galerkin-fem-code/1786)
**Author:** [@Qianrui](https://community.freefem.org/u/Qianrui)\ **Replies:** 22\ **Last updated:** [September 6, 2023, 6:00am UTC](https://community.freefem.org/t/1d-discontinuous-galerkin-fem-code/1786 "2023-09-06T06:00:44Z")
Hello, teacher, Can freefem++ write 1D discontinuous Galerkin FEM code? --- ## [Understanding problem](https://community.freefem.org/t/understanding-problem/2684)
**Author:** [@moufide](https://community.freefem.org/u/moufide)\ **Replies:** 1\ **Last updated:** [September 5, 2023, 3:39pm UTC](https://community.freefem.org/t/understanding-problem/2684 "2023-09-05T15:39:18Z")
Good evening everyone I would like to understand this code: // Parameters func u0 = 10. + 90.x/6.; func k = 1.8(y\<0.5) + 0.2; real ue = 25.; real alpha=0.25; real T=5.; real dt=0.1 ; // Mesh mesh Th = square(30… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=26) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=28)