testeigen.edp

FreeFem++可以生成高质量的有限元网格。可以用于流体力学

//  laplace with matrix  
verbosity=1;
mesh Th=square(2,2);
fespace Vh(Th,P1);
Vh u1,u2;
int n=u1.n;
real[int] Bu1(n),Bu2(n);
real[int] Au1(n),Au2(n);

real[int,int] Af(n,n),Bf(n,n),OPf(n,n);
Af=0;
Bf=0;

for(int i=0;i<n;++i)
  Bf(i,i)=1;

for(int i=0;i<n;++i)
  Af(i,i)=i;

OPf= Af;

real sigma = 0;                     


matrix OP= OPf;
matrix A=Af;
matrix B=  Bf;
int nev=n-2;

real[int] ev(nev); // to store 10 eigein value real part
real[int] evi(nev); // to store 10 eigein value imag part
Vh[int] eV(nev);   // to store 10 eigen vector  
/*
 For real nonsymmetric problems, complex eigenvectors are
 given as two consecutive vectors, so if Eigenvalue $k$ and $k+1$ 
 are complex conjugate eigenvalues, 
the vector eV[K] will contain the real part and 
the vector eV[K] the imaginary part of the corresponding 
complex conjugate eigenvectors. 
*/


int k=EigenValue(OP,B,sym=false,sigma=sigma,value=ev,vector=eV,
	         tol=1e-10,maxit=0,ncv=0,ivalue=evi);
k=min(k,nev); //  some time the number of converged eigen value 
              // can be greater than nev;
for (int kk=0;kk<k;kk++)
{ 
  int i=kk;
  u1=eV[i];
  u2=0;
  real er=ev[i],ei=evi[i];
  complex v= er+ei*1i;
  if(ei) { // complex case
    int j=++kk;
    if (j>=k) break; 
    u2 = eV[j];
  }
  cout << " ---- " <<  i<< " "  <<" eigenvalue= " << v  << endl;
  cout << " real  part " <<  u1[]  << endl;
  cout << " imag  part " <<  u2[]  << endl;

}