# La matrice de raideur lorsque la solution est un champ vectoriel

**URL:** https://community.freefem.org/t/la-matrice-de-raideur-lorsque-la-solution-est-un-champ-vectoriel/3884
**Category:** General Discussion
**Created:** [April 25, 2025, 9:17pm UTC](https://community.freefem.org/t/la-matrice-de-raideur-lorsque-la-solution-est-un-champ-vectoriel/3884 "2025-04-25T21:17:05Z")
**Posts on this page:** 1
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### Author: ![fb77](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/fb77/32/3796_2.png) [@fb77](https://community.freefem.org/u/fb77)
#### Post date: [April 26, 2025, 10:03am UTC](https://community.freefem.org/t/la-matrice-de-raideur-lorsque-la-solution-est-un-champ-vectoriel/3884/2 "2025-04-26T10:03:08Z")

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Hello,  
You have an example here:

> [@Traction Forces - BilinearOperator NM error](https://community.freefem.org/t/traction-forces-bilinearoperator-nm-error/3857/4):
>
> The problem is that the space Vh you give in matrix A = avar(Vh, Vh, tgv = -1) has not the right size, since varf avar([ur, uz], [vr, vz]) has two unknowns ur,uz. You have to set fespace Vh2(Th,[P1,P1]); Vh2 [u1,u2]; The space Vh2 has the right size. Then you correct your system resolution by matrix A = avar(Vh2, Vh2, tgv = -1); // System matrix real[int] b = Lrhs(0, Vh2); // Right-hand side vector set(A, solver = sparsesolver); real[int] sol = A^-1 \* b; u1[]=sol;// dist…

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