# Error assembling a matrix 3d surface mesh **URL:** \ **Category:** General Discussion\ **Created:** [April 9, 2020, 12:39pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325 "2020-04-09T12:39:39Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 9, 2020, 12:39pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/1 "2020-04-09T12:39:39Z")
Hello, I came across a segmentation fault when trying to get a matrix from varf when using a 3d surface mesh. The following code gives the error, using the torus given as example in the doc. I have tried with both FreeFem++4.5 and the recent 4.6. Any ideas on how to solve this ? Thank you. ``` load"msh3" real R = 3, r=1; real h = 0.2; // int nx = R*2*pi/h; int ny = r*2*pi/h; func torex= (R+r*cos(y*pi*2))*cos(x*pi*2); func torey= (R+r*cos(y*pi*2))*sin(x*pi*2); func torez= r*sin(y*pi*2); meshS ThS=square3(nx,ny,[torex,torey,torez],orientation=-1) ; fespace Vh(ThS,[P1,P1]); macro grad(u) [dx(u),dy(u),dz(u)] //EOM func f1 = 10; func f2 = -15; varf vP([u1,u2],[v1,v2]) = int2d(ThS)(grad(u1)'*grad(v1)+ grad(u2)'*grad(v2)) - int2d(ThS)(f1*v1+f2*v2); matrix A = vP(Vh,Vh); ``` ---
**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\ **Post date:** [April 9, 2020, 12:43pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/2 "2020-04-09T12:43:07Z")
```auto varf vP([u1,u2],[v1,v2]) = int2d(ThS)(grad(u1)'*grad(v1)+ grad(u2)'*grad(v2)) - int2d(ThS)(f1*v1+f2*v2); ``` ---
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 9, 2020, 1:12pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/3 "2020-04-09T13:12:53Z")
I corrected the code, thank you. ---
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 21, 2020, 12:00pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/4 "2020-04-21T12:00:27Z")
Hi, Does someone have an explanation for this? Thank you, Rémi ---
**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\ **Post date:** [April 21, 2020, 7:14pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/5 "2020-04-21T19:14:58Z")
What is the problem right now? ---
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 27, 2020, 8:00am UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/6 "2020-04-27T08:00:56Z")
The problem is: > matrix A = vP(Vh,Vh); provokes a Segmentation fault (core dumped). ---
**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\ **Post date:** [April 27, 2020, 8:12am UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/7 "2020-04-27T08:12:32Z")
Not with the correct variational formulation, does it? ---
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 27, 2020, 10:12am UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/8 "2020-04-27T10:12:39Z")
No, even with the correct formulation (I corrected it in the initial post) the error still arises. Any other clue? ---
**Author:** ![AFourmont](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/afourmont/32/56_2.png) [@AFourmont](https://community.freefem.org/u/AFourmont)\ **Post date:** [April 27, 2020, 12:30pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/9 "2020-04-27T12:30:15Z")
Hello, I amn’t able to reproduce your bug, can you give me information about your system please Do you use binary package or compile FreeFEM? ---
**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\ **Post date:** [April 27, 2020, 1:10pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/10 "2020-04-27T13:10:17Z")
Same for me: I can reproduce the segmentation fault with your initial code, but not with the new one. ---
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 27, 2020, 1:30pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/11 "2020-04-27T13:30:07Z")
Thank you for your help. I have compiled Freefem++ 4.5 on Ubuntu 18.04. ---
**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\ **Post date:** [April 27, 2020, 1:53pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/12 "2020-04-27T13:53:10Z")
Could you please try version 4.6? ---
**Author:** ![Remi](https://avatars.discourse-cdn.com/v4/letter/r/ed8c4c/32.png) [@Remi](https://community.freefem.org/u/Remi)\ **Post date:** [April 27, 2020, 2:41pm UTC](https://community.freefem.org/t/error-assembling-a-matrix-3d-surface-mesh/325/13 "2020-04-27T14:41:18Z")
Alright, it works with the 4.6 installed from the binary package. Thank you very much.