//  we have defined a matrix A and a matrix R for the eigenvector, both of dim n x n
//  The final matrix R has the eigenvectors in its row elements, it is set to one
//  for the diagonal elements in the beginning, zero else.
....
double tolerance = 1.0E-10; 
int iterations = 0;
while ( maxnondiag > tolerance && iterations <= maxiter)
{
   int p, q;
   offdiag(A, &p, &q, n);
   Jacobi_rotate(A, R, p, q, n);
   iterations++;
}
...