# General Discussion **URL:** https://community.freefem.org/c/general-discussion/7.md?page=73 [Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md) **Page:** 74 --- ## [HPDDM and Block-CG solver example](https://community.freefem.org/t/hpddm-and-block-cg-solver-example/227)
**Author:** [@ylnz7](https://community.freefem.org/u/ylnz7)\ **Replies:** 15\ **Last updated:** [January 30, 2020, 5:46am UTC](https://community.freefem.org/t/hpddm-and-block-cg-solver-example/227 "2020-01-30T05:46:12Z")
Hi, I really want to test the Block-CG method through HPDDM. I know that in FreeFem++ we can use all the features of HPDDM and it is mentioned in the tutorial that HPDDM has a Block-CG method. But I didn’t see any exampl… --- ## [Laplacian operator](https://community.freefem.org/t/laplacian-operator/218)
**Author:** [@hraf5](https://community.freefem.org/u/hraf5)\ **Replies:** 4\ **Last updated:** [January 29, 2020, 5:01pm UTC](https://community.freefem.org/t/laplacian-operator/218 "2020-01-29T17:01:28Z")
Hello every one, I want to compute the Laplacian operator of a vector u in Vh (Th, P1) finite element space. I use two different approaches: macro Laplacian(u) (dxx(u) + dyy(u)) // Vh u; Vh lap\_U = Laplacian(u); w… --- ## [HPDDM 3D periodic Cube](https://community.freefem.org/t/hpddm-3d-periodic-cube/228)
**Author:** [@abrunk](https://community.freefem.org/u/abrunk)\ **Replies:** 3\ **Last updated:** [January 21, 2020, 6:51pm UTC](https://community.freefem.org/t/hpddm-3d-periodic-cube/228 "2020-01-21T18:51:12Z")
Hi, I’m trying to use the HPDDM solver by PETSC on a full periodic cube in 3D. So far I tried to orient myself on this example: If I use the unbalanced one the mesh creation takes like forever. Unfortunately, it is… --- ## [Lgfem.cpp : pb occuring while remeshing with periodic boundary conditions](https://community.freefem.org/t/lgfem-cpp-pb-occuring-while-remeshing-with-periodic-boundary-conditions/205)
**Author:** [@JHD](https://community.freefem.org/u/JHD)\ **Replies:** 1\ **Last updated:** [January 20, 2020, 9:55am UTC](https://community.freefem.org/t/lgfem-cpp-pb-occuring-while-remeshing-with-periodic-boundary-conditions/205 "2020-01-20T09:55:35Z")
Hi Everyone, I have problems while remeshing a mesh with periodic boundary conditions. I get an error when I reinterpolate fields on the new mesh. The issue occurs with the file lgfem.cpp… but by looking at it, I am m… --- ## [Preferred way to construct block matrices with exact Dirichlet BC (tgv = -1)?](https://community.freefem.org/t/preferred-way-to-construct-block-matrices-with-exact-dirichlet-bc-tgv-1/222)
**Author:** [@cmd](https://community.freefem.org/u/cmd)\ **Replies:** 3\ **Last updated:** [January 16, 2020, 12:44am UTC](https://community.freefem.org/t/preferred-way-to-construct-block-matrices-with-exact-dirichlet-bc-tgv-1/222 "2020-01-16T00:44:54Z")
Hello, I have a composite system with several overlapping FE spaces which I construct in blocks using independent variational forms for each space and then assembling them all into a large block matrix. I would like to … --- ## [Magnetostatics inconsistent sign for current and field](https://community.freefem.org/t/magnetostatics-inconsistent-sign-for-current-and-field/125)
**Author:** [@alberto](https://community.freefem.org/u/alberto)\ **Replies:** 3\ **Last updated:** [January 14, 2020, 11:22pm UTC](https://community.freefem.org/t/magnetostatics-inconsistent-sign-for-current-and-field/125 "2020-01-14T23:22:20Z")
Hello, I downloaded the 2D example of the magnetostatic problem at https://modules.freefem.org/modules/magnetostatic/ and I have added a few lines to compute By = dy(Az) and plot its values in 2D. According to the sign … --- ## [How can I judge whether a point(x,y,z) in a given mesh?](https://community.freefem.org/t/how-can-i-judge-whether-a-point-x-y-z-in-a-given-mesh/221)
**Author:** [@Sam0012](https://community.freefem.org/u/Sam0012)\ **Replies:** 0\ **Last updated:** [January 14, 2020, 12:14pm UTC](https://community.freefem.org/t/how-can-i-judge-whether-a-point-x-y-z-in-a-given-mesh/221 "2020-01-14T12:14:13Z")
I have a mesh Th and I have a set of points(x,y,z) in the same space, but may not inside Th, How can I judge whether a point is in the mesh Th? Is there a function that receive a point and a mesh then return the judgemen… --- ## [How to impact tecplot file(dat) into freefem++](https://community.freefem.org/t/how-to-impact-tecplot-file-dat-into-freefem/217)
**Author:** [@xlzheng](https://community.freefem.org/u/xlzheng)\ **Replies:** 0\ **Last updated:** [January 13, 2020, 7:52am UTC](https://community.freefem.org/t/how-to-impact-tecplot-file-dat-into-freefem/217 "2020-01-13T07:52:00Z")
In my example, I want to compare the numerical results(from freefem++) to the analytical solutions, the analytical solutions is a dat file, I need to impact it into freefem++, but I don’t know modify the file. --- ## [Programming the Dirac mass](https://community.freefem.org/t/programming-the-dirac-mass/215)
**Author:** [@sellila](https://community.freefem.org/u/sellila)\ **Replies:** 0\ **Last updated:** [January 10, 2020, 11:36am UTC](https://community.freefem.org/t/programming-the-dirac-mass/215 "2020-01-10T11:36:23Z")
Hello, i want programming this stationary equation but i don’t know, how i can programming the right hand side of this equation -\\mu \\Delta C + (u.\\nabla)C = \\sum \\limits\_{{i=1}}^N F\_i(t)\\delta(r-r\_0) C(x,0) = C\_0 de… --- ## [Assertion fail pointed to DOperator.hpp](https://community.freefem.org/t/assertion-fail-pointed-to-doperator-hpp/211)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 1\ **Last updated:** [January 8, 2020, 1:57pm UTC](https://community.freefem.org/t/assertion-fail-pointed-to-doperator-hpp/211 "2020-01-08T13:57:07Z")
Hi, So I tried to compile the following piece of code: load "msh3" // include "ffmatlib.idp" include "utilities.idp" // mesh int N = 10; mesh3 Th = cube(N, N, N); // The finite element space defined over Th fespace V… --- ## [Explicit calculation of gradient of a scalar field](https://community.freefem.org/t/explicit-calculation-of-gradient-of-a-scalar-field/212)
**Author:** [@distractor](https://community.freefem.org/u/distractor)\ **Replies:** 0\ **Last updated:** [January 8, 2020, 1:55pm UTC](https://community.freefem.org/t/explicit-calculation-of-gradient-of-a-scalar-field/212 "2020-01-08T13:55:45Z")
So my whole problem consists of two stages: First a heat equation is solved: problem Heat(T2,v) = int3d(Th)(T2 \* v) + int3d(Th)(dt \* nu \* Grad(T2)' \* Grad(v)) - int3d(Th)(T1 \* v) +int3d(Th, 1, 2, 3,… --- ## [Negative part of a function](https://community.freefem.org/t/negative-part-of-a-function/132)
**Author:** [@paolopiers](https://community.freefem.org/u/paolopiers)\ **Replies:** 1\ **Last updated:** [January 4, 2020, 9:56pm UTC](https://community.freefem.org/t/negative-part-of-a-function/132 "2020-01-04T21:56:07Z")
Hello everyone. Today I would like to ask the following question: How do you implement, in FreeFem++, the negative part of a function defined over the integration domain of your variational equations? By definition, N… --- ## [How do I specify a boundary condition with curl?](https://community.freefem.org/t/how-do-i-specify-a-boundary-condition-with-curl/144)
**Author:** [@linwaytin](https://community.freefem.org/u/linwaytin)\ **Replies:** 1\ **Last updated:** [January 4, 2020, 9:46pm UTC](https://community.freefem.org/t/how-do-i-specify-a-boundary-condition-with-curl/144 "2020-01-04T21:46:32Z")
I’m solving TDGL on a 2D circular domain. I don’t know how to specify the boundary condition for the vector potential A. One of the BC is that curl A = B, where B is the given magnetic field. In the variational form, … --- ## [Isoparametric mesh](https://community.freefem.org/t/isoparametric-mesh/206)
**Author:** [@amina](https://community.freefem.org/u/amina)\ **Replies:** 0\ **Last updated:** [January 2, 2020, 4:56pm UTC](https://community.freefem.org/t/isoparametric-mesh/206 "2020-01-02T16:56:38Z")
Hello evryone, I am trying to figure out how to implement an iso-parametric mesh. By that I mean that my boundaries are curved and that I am seeking for an integral computation within mass and stifness matrices that tak… --- ## [How to assign locally value functions to elements in a P0 space](https://community.freefem.org/t/how-to-assign-locally-value-functions-to-elements-in-a-p0-space/204)
**Author:** [@Jacoban90](https://community.freefem.org/u/Jacoban90)\ **Replies:** 2\ **Last updated:** [December 23, 2019, 8:13pm UTC](https://community.freefem.org/t/how-to-assign-locally-value-functions-to-elements-in-a-p0-space/204 "2019-12-23T20:13:01Z")
Hi FreeFem community. Im trying to define a criteria to remove boundary elements of a 3d mesh by obtaining the number of faces in contact to an adjacent mesh. As the trunc operator needs to define previously a function … --- ## [Solve linear system A\*X=b](https://community.freefem.org/t/solve-linear-system-a-x-b/203)
**Author:** [@hraf5](https://community.freefem.org/u/hraf5)\ **Replies:** 8\ **Last updated:** [December 18, 2019, 10:20am UTC](https://community.freefem.org/t/solve-linear-system-a-x-b/203 "2019-12-18T10:20:39Z")
Hi every one, I have a linear system A\*X=b… Is there any command to solve it directly in FreeFem++ ? Thanks. --- ## [Mesh problem bad sens](https://community.freefem.org/t/mesh-problem-bad-sens/195)
**Author:** [@wiam](https://community.freefem.org/u/wiam)\ **Replies:** 3\ **Last updated:** [December 17, 2019, 4:48pm UTC](https://community.freefem.org/t/mesh-problem-bad-sens/195 "2019-12-17T16:48:09Z")
help please ,i cant mesh my space "Meshing error: Bamg number : 777, " bad sens and i dont know where the problem is i checked in every common poit its verifies that the space is closed this is my program //datas i… --- ## [Laplace-Beltrami on surfaces](https://community.freefem.org/t/laplace-beltrami-on-surfaces/202)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 2\ **Last updated:** [December 17, 2019, 4:45pm UTC](https://community.freefem.org/t/laplace-beltrami-on-surfaces/202 "2019-12-17T16:45:16Z")
Hello. I tried to solve the Laplace Beltrami eigenvalue problem on the sphere. The usual syntax for storing the eigenfunction does not seem to work. The eigenvalues are captured correctly, but when using vector=eV I get… --- ## [Compute quantity in terms of N.x and N.y on boundary](https://community.freefem.org/t/compute-quantity-in-terms-of-n-x-and-n-y-on-boundary/190)
**Author:** [@BeniaminBogosel](https://community.freefem.org/u/BeniaminBogosel)\ **Replies:** 2\ **Last updated:** [December 6, 2019, 10:39pm UTC](https://community.freefem.org/t/compute-quantity-in-terms-of-n-x-and-n-y-on-boundary/190 "2019-12-06T22:39:56Z")
Hello, I would like to compute a quantity of the form atan2(N.y,N.x) on the boundary. I need to store this and use it multiple times in my code. (It allows me to find a reverse parametrization…) Can you suggest a way t… --- ## [Define the trace operator](https://community.freefem.org/t/define-the-trace-operator/191)
**Author:** [@hgauss](https://community.freefem.org/u/hgauss)\ **Replies:** 1\ **Last updated:** [December 4, 2019, 8:57pm UTC](https://community.freefem.org/t/define-the-trace-operator/191 "2019-12-04T20:57:41Z")
Hi ! Is there a way or a predefined function to define the trace operator ? For a given fem function u, I would like to define its restriction to the boundary. Thank you. --- ## [Gram–Schmidt process](https://community.freefem.org/t/gram-schmidt-process/189)
**Author:** [@hraf5](https://community.freefem.org/u/hraf5)\ **Replies:** 4\ **Last updated:** [December 3, 2019, 1:03pm UTC](https://community.freefem.org/t/gram-schmidt-process/189 "2019-12-03T13:03:40Z")
Hello everybody, I am trying to orthonormalize a basis using the Gram-Schmidt process. Is it possible with FreeFem ++? Thank you. --- ## [Print out the Stiffness Matrix for a vectorial variational problem](https://community.freefem.org/t/print-out-the-stiffness-matrix-for-a-vectorial-variational-problem/187)
**Author:** [@Smerdjakov](https://community.freefem.org/u/Smerdjakov)\ **Replies:** 4\ **Last updated:** [December 2, 2019, 8:56pm UTC](https://community.freefem.org/t/print-out-the-stiffness-matrix-for-a-vectorial-variational-problem/187 "2019-12-02T20:56:35Z")
Hi there, I am an absolute novice to FREEFEM++, and I cannot figure out how to (efficiently) obtain the stiffness matrix. I found in the documentation reference to the following code varf a(u,v) = int2d(Th)( dx(u)\*d… --- ## [Finite Element Method in Aeroelasticity (Flutter)](https://community.freefem.org/t/finite-element-method-in-aeroelasticity-flutter/186)
**Author:** [@81735152](https://community.freefem.org/u/81735152)\ **Replies:** 0\ **Last updated:** [December 1, 2019, 12:56pm UTC](https://community.freefem.org/t/finite-element-method-in-aeroelasticity-flutter/186 "2019-12-01T12:56:31Z")
Dear Frederic I’m working on a fluid structure interaction problem , its an airfoil on air flow to simulate the flutter phenomenon. The problem consist on solve the Navier Stokes equations couple to system of nonlinea… --- ## [Point values of unknown fespace functions in variational form](https://community.freefem.org/t/point-values-of-unknown-fespace-functions-in-variational-form/177)
**Author:** [@cmd](https://community.freefem.org/u/cmd)\ **Replies:** 2\ **Last updated:** [November 29, 2019, 6:44pm UTC](https://community.freefem.org/t/point-values-of-unknown-fespace-functions-in-variational-form/177 "2019-11-29T18:44:21Z")
Hello, I am iteratively solving a flow problem with a nonlinear forcing term which is dependent on the value of the solution at a boundary. I use Newton’s method to solve, but as I have not yet figured out how to implem… --- ## [Droplet Contact Angle Simulation](https://community.freefem.org/t/droplet-contact-angle-simulation/185)
**Author:** [@robin997](https://community.freefem.org/u/robin997)\ **Replies:** 0\ **Last updated:** [November 28, 2019, 1:37am UTC](https://community.freefem.org/t/droplet-contact-angle-simulation/185 "2019-11-28T01:37:46Z")
Hello everybody. Just wondering if anyone has tried simulating contact angle in FreeFEM before. I have tried this model from the past FreeFEM day, but I am stuck on where or how to apply the contact angle boundary condit… --- ## [How i can programming this term](https://community.freefem.org/t/how-i-can-programming-this-term/184)
**Author:** [@sellila](https://community.freefem.org/u/sellila)\ **Replies:** 2\ **Last updated:** [November 23, 2019, 7:17pm UTC](https://community.freefem.org/t/how-i-can-programming-this-term/184 "2019-11-23T19:17:23Z")
Hello everyone, i need help because, i am begineer in Freefem++ There are someone can help me, how i can programming this term a|u|^{\\alpha}u where |u| is the norm on the unknown function |u| = sqrt(ux^² + uy) Thank… --- ## [How Freefem++ assemble the forms with variable coefficient?](https://community.freefem.org/t/how-freefem-assemble-the-forms-with-variable-coefficient/178)
**Author:** [@Psywah](https://community.freefem.org/u/Psywah)\ **Replies:** 3\ **Last updated:** [November 19, 2019, 3:59pm UTC](https://community.freefem.org/t/how-freefem-assemble-the-forms-with-variable-coefficient/178 "2019-11-19T15:59:09Z")
Hello, I want to make clear about how FreeFEM deal with the variable coefficient while assembling. Here is an example: $$ a(u, v) = \\int c \\nabla u \\cdot \\nabla v $$ where c = \\cos (x) is a given function. Is there … --- ## [How to apply the GMSH boundary label in FreeFEM](https://community.freefem.org/t/how-to-apply-the-gmsh-boundary-label-in-freefem/167)
**Author:** [@Dylan](https://community.freefem.org/u/Dylan)\ **Replies:** 12\ **Last updated:** [November 11, 2019, 12:04pm UTC](https://community.freefem.org/t/how-to-apply-the-gmsh-boundary-label-in-freefem/167 "2019-11-11T12:04:41Z")
Dear developers, How to apply the boundary labels from an external mesh generator such as GMSH? The boundary patches are identified in the Gmsh step using its Physical Surface command. I import the gmsh to freefem++, … --- ## [Replicate int2d calculation](https://community.freefem.org/t/replicate-int2d-calculation/174)
**Author:** [@nish-ant](https://community.freefem.org/u/nish-ant)\ **Replies:** 0\ **Last updated:** [November 6, 2019, 12:49pm UTC](https://community.freefem.org/t/replicate-int2d-calculation/174 "2019-11-06T12:49:39Z")
I am trying to understand how the numerical integration works when we use different quadrature formulations. I have created a minimal example which calculates a correlation matrix for a very simple lid driven cavity case… --- ## [Convert variable to mixed element form](https://community.freefem.org/t/convert-variable-to-mixed-element-form/169)
**Author:** [@nish-ant](https://community.freefem.org/u/nish-ant)\ **Replies:** 1\ **Last updated:** [November 5, 2019, 7:24pm UTC](https://community.freefem.org/t/convert-variable-to-mixed-element-form/169 "2019-11-05T19:24:20Z")
I am following the tutorial on transient Stokes solver. In the last code snippet, I find the following line: w1\[\]=sol; u=w1; v= w2; p=wp; which saves the solution from w1\[\] corresponding to a P2,P2,P1 mixed space to in… [Previous page](https://community.freefem.org/c/general-discussion/7.md?page=72) [Next page](https://community.freefem.org/c/general-discussion/7.md?page=74)