fft的实现

 1     private static Complex[] FFT1(Complex[] f)

 2     {

 3         int N=f.length;

 4         int power= (int) (Math.log10(N)/Math.log10(2));

 5         Complex[] F=new Complex[N];

 6         //按奇偶分组

 7         for(int i=0;i<N;i++)

 8         {

 9             int p = 0;  

10             for (int j = 0; j < power; j++)  

11                 if ((i & (1 << j)) != 0)  

12                     p += 1 << (power - j - 1);  

13 

14             F[p] = f[i];

15         }

16         //蝶形因子

17         Complex[] wc = new Complex[N/ 2];

18         for (int i = 0; i < N / 2; i++)

19         {

20             double angle = -i * Math.PI * 2 / N;

21             wc[i]=new Complex(Math.cos(angle),Math.sin(angle));

22         }

23         //蝶形运算

24         for(int L=1;L<=power;L++)//第L层数

25         {

26             int bf=1<<(power-L);//蝶形数

27             for(int n=0;n<bf;n++)//第n+1个蝶形

28             {

29                 int bfsize=1<<L;//蝶形大小

30                 for(int k=0;k<bfsize/2;k++)//第k+1个蝶形因子

31                 {

32                     Complex temp,X1,X2;;

33                     int i=n*bfsize+k,

34                         j=i+bfsize/2;

35                     temp=wc[k*bf].Mul(F[j]);

36                     X1=F[i].Add(temp);

37                     X2=F[i].Sub(temp);

38                     F[i]=X1;

39                     F[j]=X2;

40                 }            

41             }

42         }

43         return F;

44     }