@Test
public void testSomeMethod() {

    int N=180;
    DirichletKernel dk=new DirichletKernel(N);
    double step=Math.PI*2/N;
    double z=0;
    for (int i=1; i<20; ++i){
        double k=dk.fn(step*i);
        z+=k*k*step*Math.PI*2;
    }
      double dn=N;
      for (int i=20; i<N/2; ++i){
          double k=dk.fn(step*i);
          z+=k*k*step*Math.PI*2;
          System.out.print(z);
          System.out.print('\t');
          System.out.println(i/dn);
      }
}