# What's wrong with my code
**URL:** https://community.freefem.org/t/whats-wrong-with-my-code/3902
**Category:** General Discussion
**Created:** [May 6, 2025, 11:01am UTC](https://community.freefem.org/t/whats-wrong-with-my-code/3902 "2025-05-06T11:01:41Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@BelfaidaMedReda](https://community.freefem.org/u/BelfaidaMedReda)
#### Post date: [May 6, 2025, 11:01am UTC](https://community.freefem.org/t/whats-wrong-with-my-code/3902/1 "2025-05-06T11:01:41Z")
Hello, I’m new to freefem, I can’t compute the eigenvalues as I’m getting this error
71 : varf a(u, v) = int2d(T)( dx(u) unknown operator ( on type
Error line number 71, in file drum\_shapestest.edp, before token )
current line = 71
Compile error :
line number :71, )
error Compile error :
line number :71, )
code = 1 mpirank: 0
real L = 1;
// Définir les bords du triangle (3 segments)
border alpha1(t=0, L){ x=t; y=0; label=1; }
border beta1(t=0, L){ x=L; y=t; label=2; }
border gamma1(t=0, L){ x=(1-t)\*L; y=(1-t)\*L; label=3; }
// Maillage avec 10 points par bord
mesh T1 = buildmesh(beta1(10) + gamma1(10) + alpha1(10));
border alpha2(t=0,L){ x=0; y=L - t; label=4; }
border beta2(t=0,L){ x=L - t; y=L; label=5; }
border gamma2(t=0,L){ x=t_L; y=t_L; label=6; }
mesh T2 = buildmesh(gamma2(10) + beta2(10) + alpha2(10));
// Triangle T3
border beta3(t=0,L){ x=-L; y = L + t;label=16;}
border alpha3(t=0,L) { x= -L-t; y=2_L;label=17;}
border gamma3(t=0,1){ x= -2_L\*(1-t)-L_t; y = 2_L\*(1-t) + t\*L;label=18;}
mesh T3 = buildmesh(beta3(10)+alpha3(10)+gamma3(10));
// Triangle T4
border alpha4(t=0, L){ x=0; y=2\*L - t; label=13; }
border beta4(t=0, L){ x=t; y=L; label=14; }
border gamma4(t=0, 1){ x=(1 - t)_L; y=(1 - t)L + t2_L; label=15; }
mesh T4 = buildmesh( beta4(10) + gamma4(10) + alpha4(10) ); // ordre anti-horaire
// Translation : -L en x, +L en y
real dx = -L;
real dy = +L;
// Triangle T6 : translation de T1
border alpha6(t=0, L){ x=t + dx; y=0 + dy; label=7; }
border beta6(t=0, L){ x=L + dx; y=t + dy; label=8; }
border gamma6(t=0, L){ x=(1-t)\*L + dx; y=(1-t)\*L + dy; label=9; }
mesh T6 = buildmesh(beta6(10) + gamma6(10) + alpha6(10));
// Triangle T5 : translation de T2
border alpha5(t=0,L){ x=0 + dx; y=L - t + dy; label=10; }
border beta5(t=0,L){ x=L - t + dx; y=L + dy; label=11; }
border gamma5(t=0,L){ x=t_L + dx; y=t_L + dy; label=12; }
mesh T5 = buildmesh(gamma5(10) + beta5(10) + alpha5(10));
// Triangle T7
border beta7(t=0,L){x=-L;y=3_L-t;label=19;}
border alpha7(t=0,L){x=-L+t;y=2_L;label=20;}
border gamma7(t=0,1){x=-t_L;y=2_L\*(1-t) + 3_t_L;label=21;}
mesh T7 = buildmesh(beta7(10) + alpha7(10) +gamma7(10));
// Fusion des 7 triangles
mesh T = T1 + T2 + T6 + T5 + T4 + T3 + T7;
// Espace de fonctions P1 avec conditions de Dirichlet automatiques
fespace Vh(T, P1);
Vh u, v;
// Définir les matrices de rigidité (a) et de masse (b)
varf a(u, v) = int2d(T)( dx(u)\*dx(v) + dy(u)_dy(v) ); // matrice raideur
varf b(u, v) = int2d(T)( u_v ); // matrice masse
// Assemblage des matrices
matrix A = a(Vh, Vh, solver=sparsesolver);
matrix B = b(Vh, Vh, solver=sparsesolver);
// Calcul des n premières valeurs propres
int nev = 5; // nombre de valeurs propres
real[int] ev(nev); // tableau pour stocker les valeurs propres
Vh[int] eVec(nev); // tableau pour stocker les vecteurs propres
// Solveur des valeurs propres (resolvent: EVP)
cout \<\< “Résolution du problème aux valeurs propres…” \<\< endl;
int k = EigenValue(A, B, sym=true, sigma=0.0, value=ev, vector=eVec);
// Affichage des valeurs propres trouvées
cout \<\< “Valeurs propres approchées (lambda):” \<\< endl;
for (int i = 0; i \< k; ++i)
cout \<\< “λ\_” \<\< i+1 \<\< " = " \<\< ev[i] \<\< endl;
// Visualisation du 1er vecteur propre
plot(eVec[0], wait=true, cmm=“1er vecteur propre”);
---
### Author:  [@fb77](https://community.freefem.org/u/fb77)
#### Post date: [May 6, 2025, 11:55am UTC](https://community.freefem.org/t/whats-wrong-with-my-code/3902/2 "2025-05-06T11:55:48Z")
Hello,
the problem is that you should not define
```auto
real dx = -L;
real dy = +L;
```
because your definitions of dx and dy hide the operators dx, dy that you want to use.
---
### Author:  [@BelfaidaMedReda](https://community.freefem.org/u/BelfaidaMedReda)
#### Post date: [May 6, 2025, 1:14pm UTC](https://community.freefem.org/t/whats-wrong-with-my-code/3902/3 "2025-05-06T13:14:31Z")
thank you so much, I realized now what was the issue!