# General Discussion

**URL:** https://community.freefem.org/c/general-discussion/7.md?page=58

[Latest](https://community.freefem.org/latest.md) · [Categories](https://community.freefem.org/categories.md)

**Page:** 59

---

## [Integrate Solution over an interior "Slice"](https://community.freefem.org/t/integrate-solution-over-an-interior-slice/1107)

<div class="topic-metadata">

**Author:** [@kevinmo08](https://community.freefem.org/u/kevinmo08)\
**Replies:** 2\
**Last updated:** [July 19, 2021, 8:41pm UTC](https://community.freefem.org/t/integrate-solution-over-an-interior-slice/1107 "2021-07-19T20:41:41Z")

</div>

Dear All, I am interested in finding the average value of a “slice”, where it cuts through the middle of my mesh. I am aware that FreeFEM allows you to integrate functions over borders using int2D for a 3D mesh or int1…

---

## [How to use notaregion (identify if a point is within the domain)](https://community.freefem.org/t/how-to-use-notaregion-identify-if-a-point-is-within-the-domain/1105)

<div class="topic-metadata">

**Author:** [@hezl09](https://community.freefem.org/u/hezl09)\
**Replies:** 2\
**Last updated:** [July 19, 2021, 6:19pm UTC](https://community.freefem.org/t/how-to-use-notaregion-identify-if-a-point-is-within-the-domain/1105 "2021-07-19T18:19:11Z")

</div>

Hi everyone, I’m trying to identify if a point is in a working domain or not, so I write the following simple code: mesh Th; Th = square(10,10,\[0.+1.\*x,0.+1.\*y\],region=1); plot(Th); cout \<\< "point (0.5,0.5) has a re…

---

## [The integral mesh and the mesh associated to test functions or unknown functions can be different in the case of varf form](https://community.freefem.org/t/the-integral-mesh-and-the-mesh-associated-to-test-functions-or-unknown-functions-can-be-different-in-the-case-of-varf-form/1103)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 0\
**Last updated:** [July 19, 2021, 10:14am UTC](https://community.freefem.org/t/the-integral-mesh-and-the-mesh-associated-to-test-functions-or-unknown-functions-can-be-different-in-the-case-of-varf-form/1103 "2021-07-19T10:14:00Z")

</div>

Dear all, I read from the FreeFem document (page 202, release 4.6) that " The integral mesh and the mesh associated to test functions or unknown functions can be different in the case of varf form". I am wondering what…

---

## [Preconditioner for PETSc Mat](https://community.freefem.org/t/preconditioner-for-petsc-mat/1096)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 7\
**Last updated:** [July 18, 2021, 10:06pm UTC](https://community.freefem.org/t/preconditioner-for-petsc-mat/1096 "2021-07-18T22:06:53Z")

</div>

Deat all, How to specify a block preconditioner in PETSc. For example, specify preconditioner P= A 0 0 M for solving Kx=b, with K= A B B’ 0 Best, Yongxing.

---

## [How to 1d intergrate along x/y direction in 2d mesh](https://community.freefem.org/t/how-to-1d-intergrate-along-x-y-direction-in-2d-mesh/986)

<div class="topic-metadata">

**Author:** [@xlzheng](https://community.freefem.org/u/xlzheng)\
**Replies:** 4\
**Last updated:** [July 18, 2021, 2:26pm UTC](https://community.freefem.org/t/how-to-1d-intergrate-along-x-y-direction-in-2d-mesh/986 "2021-07-18T14:26:28Z")

</div>

Now 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. Then I want to know the line integral of u along y to get ∫𝑢𝑑𝑦, but I don’t know how to implement …

---

## [Hydrodynamic Stability Implementation in FreeFEM](https://community.freefem.org/t/hydrodynamic-stability-implementation-in-freefem/622)

<div class="topic-metadata">

**Author:** [@D\_N\_Sarkar](https://community.freefem.org/u/D_N_Sarkar)\
**Replies:** 22\
**Last updated:** [July 18, 2021, 9:35am UTC](https://community.freefem.org/t/hydrodynamic-stability-implementation-in-freefem/622 "2021-07-18T09:35:15Z")

</div>

I am trying to carry out 3-D hydrodynamic stability analysis of 2-dimensional lid-driven square cavity flow at Re = 200. I have calculated the 2-dimensional base flow at Re=200 and validated the base flow results with e…

---

## [Problem interpolating between meshes](https://community.freefem.org/t/problem-interpolating-between-meshes/1074)

<div class="topic-metadata">

**Author:** [@lparras](https://community.freefem.org/u/lparras)\
**Replies:** 3\
**Last updated:** [July 15, 2021, 7:58pm UTC](https://community.freefem.org/t/problem-interpolating-between-meshes/1074 "2021-07-15T19:58:30Z")

</div>

Dear all. I am having an issue interpolating between two meshes. I have a first mesh like the first figure provided by other code . I have defined a mesh in the same domain (in FreeFem) and interpolated the data fro…

---

## [Calculate on variable depth scalar field](https://community.freefem.org/t/calculate-on-variable-depth-scalar-field/1077)

<div class="topic-metadata">

**Author:** [@Antonin\_a](https://community.freefem.org/u/Antonin_a)\
**Replies:** 1\
**Last updated:** [July 14, 2021, 1:28pm UTC](https://community.freefem.org/t/calculate-on-variable-depth-scalar-field/1077 "2021-07-14T13:28:46Z")

</div>

Hello everyone, In order to solver a simple mildslope equation (in 2D), I’d like to make calculation over a bathymetry (variable depth). I have a grid with the coordinates x, y, z . My problem is in the mildslope equat…

---

## [A+B and its sparsity](https://community.freefem.org/t/a-b-and-its-sparsity/1094)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 3\
**Last updated:** [July 13, 2021, 8:53am UTC](https://community.freefem.org/t/a-b-and-its-sparsity/1094 "2021-07-13T08:53:28Z")

</div>

When we add matrix B to A (PETSc Mat), is there a method to drop the non-zero elements in B which do not exist in A? For example, if A= \[ 1, 0 0, 2\] B= \[1, -1 0, 3\] Can we neglect -1 in B, so that B would have t…

---

## [How assignment operator works for discontinuous fields](https://community.freefem.org/t/how-assignment-operator-works-for-discontinuous-fields/1093)

<div class="topic-metadata">

**Author:** [@arousta](https://community.freefem.org/u/arousta)\
**Replies:** 0\
**Last updated:** [July 12, 2021, 7:50pm UTC](https://community.freefem.org/t/how-assignment-operator-works-for-discontinuous-fields/1093 "2021-07-12T19:50:54Z")

</div>

The documentation says the = operator does interpolation. But not clear on what happens when interpolating discontinuous fields. For example: mesh Th = square(1,1); fespace Vh0(Th,P0); fespace Vh1(Th,P1); Vh0 F0 = x; V…

---

## [Additive Manufacturing Modeling](https://community.freefem.org/t/additive-manufacturing-modeling/609)

<div class="topic-metadata">

**Author:** [@Stephan](https://community.freefem.org/u/Stephan)\
**Replies:** 1\
**Last updated:** [July 11, 2021, 4:40pm UTC](https://community.freefem.org/t/additive-manufacturing-modeling/609 "2021-07-11T16:40:37Z")

</div>

Hello everyone, I am very new to FEM programs and am currently trying to study the process of additive manufacturing of metals. Ultimately, I am trying to have a multi physics solver that is able to model the thermal pr…

---

## [Levelset Dirichlet Condition in 3d on phi=0 surface](https://community.freefem.org/t/levelset-dirichlet-condition-in-3d-on-phi-0-surface/1091)

<div class="topic-metadata">

**Author:** [@Jonas\_Zille](https://community.freefem.org/u/Jonas_Zille)\
**Replies:** 0\
**Last updated:** [July 11, 2021, 4:34pm UTC](https://community.freefem.org/t/levelset-dirichlet-condition-in-3d-on-phi-0-surface/1091 "2021-07-11T16:34:47Z")

</div>

Dear All, I hope you can help me with the following problem. I have a mesh (3d) where there is a rather sharp levelset function “phi” defined by scalar values (threshold). I have found the method int2d(Th,levelset=phi…

---

## [Assertion fail: femlib/GQuadTree.cpp](https://community.freefem.org/t/assertion-fail-femlib-gquadtree-cpp/1089)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 8\
**Last updated:** [July 11, 2021, 12:21am UTC](https://community.freefem.org/t/assertion-fail-femlib-gquadtree-cpp/1089 "2021-07-11T00:21:31Z")

</div>

Dear all, I am sure the displacement is very small, however when I do Ths=movemesh(Ths0, \[x+dispx,y+dispy,z+dispz\]); // Ths0 is an initial mesh it always has the following error after several time stesp: Does any…

---

## [Assertion fail: (nbdeja\<100)](https://community.freefem.org/t/assertion-fail-nbdeja-100/1088)

<div class="topic-metadata">

**Author:** [@Daokun](https://community.freefem.org/u/Daokun)\
**Replies:** 1\
**Last updated:** [July 8, 2021, 8:17am UTC](https://community.freefem.org/t/assertion-fail-nbdeja-100/1088 "2021-07-08T08:17:59Z")

</div>

Hi guys, My codes worked fine last week. suddenly, an error notification called “assertion fail: (nbdeja\<100) line 831: in file …/femlib/GQuadTree.cpp” occurrs this week with same codes. Does anyone knows what this …

---

## [Manually Refine Mesh near boundary](https://community.freefem.org/t/manually-refine-mesh-near-boundary/1087)

<div class="topic-metadata">

**Author:** [@kevinmo08](https://community.freefem.org/u/kevinmo08)\
**Replies:** 0\
**Last updated:** [July 6, 2021, 7:16pm UTC](https://community.freefem.org/t/manually-refine-mesh-near-boundary/1087 "2021-07-06T19:16:58Z")

</div>

Hi all, I am attempting to solve a convection diffusion equation in FreeFEM using the built in mesh software. I have found that splitmesh allows me to refine a mesh based on the functional form I input to it. However, …

---

## [How can i mute PETSc?](https://community.freefem.org/t/how-can-i-mute-petsc/1079)

<div class="topic-metadata">

**Author:** [@mazzman](https://community.freefem.org/u/mazzman)\
**Replies:** 7\
**Last updated:** [July 6, 2021, 3:40pm UTC](https://community.freefem.org/t/how-can-i-mute-petsc/1079 "2021-07-06T15:40:13Z")

</div>

How can I mute the messages coming from PETSc such as " — system solved with PETSc (in …)"? Can I use verbosity to only print my cout massages to the console?

---

## [Error: border points to close](https://community.freefem.org/t/error-border-points-to-close/534)

<div class="topic-metadata">

**Author:** [@SB44](https://community.freefem.org/u/SB44)\
**Replies:** 1\
**Last updated:** [July 5, 2021, 6:15pm UTC](https://community.freefem.org/t/error-border-points-to-close/534 "2021-07-05T18:15:19Z")

</div>

In my script I want to create a mesh from points, read from a .txt file. However I get the error: Exec error : Error points border points to close \< diameter\*1e-7 – number :1 I have looked for a solution, but could …

---

## [Interface Conditions Implementation](https://community.freefem.org/t/interface-conditions-implementation/1083)

<div class="topic-metadata">

**Author:** [@sumantkr](https://community.freefem.org/u/sumantkr)\
**Replies:** 0\
**Last updated:** [July 5, 2021, 4:44pm UTC](https://community.freefem.org/t/interface-conditions-implementation/1083 "2021-07-05T16:44:18Z")

</div>

Hello Everyone Can anyone suggest me to implement the interface boundary conditions of a domain made with two or more subdomains? Any sample code may help me to solve my problem. Thanks in advance!!!

---

## [FreeFem interpolation](https://community.freefem.org/t/freefem-interpolation/1082)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 1\
**Last updated:** [July 5, 2021, 9:59am UTC](https://community.freefem.org/t/freefem-interpolation/1082 "2021-07-05T09:59:11Z")

</div>

Dear all, When using interpolate() or transferMat(), the interpolation matrix is always a linear interpolation, or the interpolation uses FEM shape function (therefore it could be high order interpolation for the high o…

---

## [Pass value between different vector fespaces](https://community.freefem.org/t/pass-value-between-different-vector-fespaces/1067)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 1\
**Last updated:** [July 2, 2021, 3:49am UTC](https://community.freefem.org/t/pass-value-between-different-vector-fespaces/1067 "2021-07-02T03:49:42Z")

</div>

Dear all, if we have Vh fespace (Th, \[P2, P2, P1\]); Wh fespace (Th, \[P2,P2\]); Vh \[ux, uy, p\]; Wh \[wx, wy\]; After moving the mesh of Th, what shall we usually do if want to pass the nodal values of ux and uy to wx…

---

## [Plasticity model in FreeFem++](https://community.freefem.org/t/plasticity-model-in-freefem/1075)

<div class="topic-metadata">

**Author:** [@distractor](https://community.freefem.org/u/distractor)\
**Replies:** 0\
**Last updated:** [July 1, 2021, 8:08pm UTC](https://community.freefem.org/t/plasticity-model-in-freefem/1075 "2021-07-01T20:08:39Z")

</div>

Hi, I am having real problems with plastic body deformation. I am so stuck that I actually don’t even know what to answer. So my case is I have a stress(plastic strain, temperature) data table, and now I have to implem…

---

## [Memory issue with Parallel computing](https://community.freefem.org/t/memory-issue-with-parallel-computing/1072)

<div class="topic-metadata">

**Author:** [@zcwang6](https://community.freefem.org/u/zcwang6)\
**Replies:** 17\
**Last updated:** [July 1, 2021, 5:07pm UTC](https://community.freefem.org/t/memory-issue-with-parallel-computing/1072 "2021-07-01T17:07:58Z")

</div>

Dear FreeFem team, I have been using FreeFem PETSc framework to do my research. Currently, I noticed there was a memory accumulation problem when I increases the threads numbers. I think the problem is from below: real\[…

---

## [Graphics with FF++](https://community.freefem.org/t/graphics-with-ff/1061)

<div class="topic-metadata">

**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\
**Replies:** 1\
**Last updated:** [June 29, 2021, 7:21pm UTC](https://community.freefem.org/t/graphics-with-ff/1061 "2021-06-29T19:21:58Z")

</div>

Hi! please what instructions we have to use to plot U(x,y,t) for t fixed? We have mesh Th = square(N,N,\[L\*x,H\*y\]); fespace Vh(Th,P1); Vh U; I try to use ofstream foutU("U.txt"); for (real t=0;t\<T;t+=dt) { foutU \<\< t…

---

## [Docker images by singularity](https://community.freefem.org/t/docker-images-by-singularity/950)

<div class="topic-metadata">

**Author:** [@yongxing](https://community.freefem.org/u/yongxing)\
**Replies:** 8\
**Last updated:** [June 30, 2021, 7:58am UTC](https://community.freefem.org/t/docker-images-by-singularity/950 "2021-06-30T07:58:03Z")

</div>

Dear all, Did someone run FreeFEM using singularity? I tried: singularity build --sandbox freefem docker://freefem/freefem singularity run freefem and came across the following error: ls: cannot access ‘/data/\*.edp…

---

## [Exec MUMPS\_mpi error with Edge13d](https://community.freefem.org/t/exec-mumps-mpi-error-with-edge13d/1031)

<div class="topic-metadata">

**Author:** [@niaa](https://community.freefem.org/u/niaa)\
**Replies:** 2\
**Last updated:** [June 29, 2021, 2:12pm UTC](https://community.freefem.org/t/exec-mumps-mpi-error-with-edge13d/1031 "2021-06-29T14:12:33Z")

</div>

Hello every one, I have a problem who works with Edge03d . but when I change it to Edge13d it gives me an execution error : Erreur Mumps mpi: number -13 Fatal Erreur MUMPS\_mpi Factorize current line = 496 mpirank 0 …

---

## [Using FreeFEM for Numerical Integration](https://community.freefem.org/t/using-freefem-for-numerical-integration/1069)

<div class="topic-metadata">

**Author:** [@no6](https://community.freefem.org/u/no6)\
**Replies:** 0\
**Last updated:** [June 28, 2021, 6:54pm UTC](https://community.freefem.org/t/using-freefem-for-numerical-integration/1069 "2021-06-28T18:54:57Z")

</div>

I am new to FreeFEM but am looking for help with a 3D numerical integration. My dataset currently has x,y,z and f(x,y,z) for a total of 4 values per point. For my testing, I am applying a simple formula (such as x^2 + y^…

---

## [Parallelization save data](https://community.freefem.org/t/parallelization-save-data/1066)

<div class="topic-metadata">

**Author:** [@yhao](https://community.freefem.org/u/yhao)\
**Replies:** 2\
**Last updated:** [June 28, 2021, 6:22pm UTC](https://community.freefem.org/t/parallelization-save-data/1066 "2021-06-28T18:22:36Z")

</div>

Dear all, I am now using PETSc for solving the Navier-Stokes equation in 16 cores, but when I want to save the data of the velocity for x=0.5 (export as a txt file), it always repeatedly store some parts that are repeat…

---

## [Question about Variational Formulation](https://community.freefem.org/t/question-about-variational-formulation/1059)

<div class="topic-metadata">

**Author:** [@Aicha](https://community.freefem.org/u/Aicha)\
**Replies:** 1\
**Last updated:** [June 27, 2021, 11:02am UTC](https://community.freefem.org/t/question-about-variational-formulation/1059 "2021-06-27T11:02:51Z")

</div>

Hi! i have two questions please Q\_T = \[0,L\] x \[0,H\] x \[0,T\] 1- We have the following variational formulation: \\int\_{Q\_T} dV/dt \\psi dx dy dt = - D \\int\_{Q\_T} \\nabla V . \\nabla \\psi dx dy dt + D \\int\_0^T \\int\_0^L \\psi…

---

## [Is varf parallel? Can it be sped up?](https://community.freefem.org/t/is-varf-parallel-can-it-be-sped-up/1060)

<div class="topic-metadata">

**Author:** [@mazzman](https://community.freefem.org/u/mazzman)\
**Replies:** 2\
**Last updated:** [June 25, 2021, 6:28pm UTC](https://community.freefem.org/t/is-varf-parallel-can-it-be-sped-up/1060 "2021-06-25T18:28:00Z")

</div>

Hello, Is varf parallel and can it be sped up? I need to do transient analysis where I have to recalculate the Matrix and rhs in every time step because parameters change over time. varf seems to be the bottle neck here…

---

## [Poor results with PETSc](https://community.freefem.org/t/poor-results-with-petsc/1058)

<div class="topic-metadata">

**Author:** [@mazzman](https://community.freefem.org/u/mazzman)\
**Replies:** 4\
**Last updated:** [June 24, 2021, 5:53pm UTC](https://community.freefem.org/t/poor-results-with-petsc/1058 "2021-06-24T17:53:50Z")

</div>

Hello, I implemented a transient 3D piezoanalysis that works fine with problem. Now, I want to accelerate the simulation by using a parallel solver. However, I can’t get proper results using PETSc. The results seem to n…

[Previous page](https://community.freefem.org/c/general-discussion/7.md?page=57)

[Next page](https://community.freefem.org/c/general-discussion/7.md?page=59)