快速傅立葉變換(FFT) C

1、快速傅立葉變換（FFT）的C#代碼這個代碼是從快速傅立葉變換（FFT）的C+實現(xiàn)與Matlab實驗這篇文章里的源代碼轉(zhuǎn)換而來，請注意查看原文。在這里自己轉(zhuǎn)換成了C#代碼，并作了一些改動，主要是對N值的確定，原文的N值為常量1024，自己通過對輸入的數(shù)組的長度來確定N值，N值的確定符合2的n次方，函數(shù)返回N值。通過作者提供的測試變量進行測試，能得到相應的結(jié)果。代碼如下：FFT代碼：namespace ConsoleApplication1    / <summary>    / 快速傅立葉變換(Fast Fourier Tr

2、ansform)。     / </summary>    public class TWFFT            private TWFFT()                        priva

3、te static void bitrp(float xreal, float ximag, int n)                    / 位反轉(zhuǎn)置換 Bit-reversal Permutation            int i, j, a, b, p;   &#

4、160;        for (i = 1, p = 0; i < n; i *= 2)                            p+;         &#

5、160;              for (i = 0; i < n; i+)                            a = i;     

6、60;          b = 0;                for (j = 0; j < p; j+)                     

7、;               b = b * 2 + a % 2;                    a = a / 2;            

8、;                    if (b > i)                              &

9、#160;     float t = xreali;                    xreali = xrealb;                    xrealb

10、= t;                    t = ximagi;                    ximagi = ximagb;      

11、60;             ximagb = t;                                      

12、      public static int FFT(float xreal, float ximag)                    /n值為2的N次方            int n = 2;    &#

13、160;       while (n <= xreal.Length)                            n *= 2;           

14、             n /= 2;            / 快速傅立葉變換，將復數(shù) x 變換后仍保存在 x 中，xreal, ximag 分別是 x 的實部和虛部            float wreal = new floatn / 2; 

15、60;          float wimag = new floatn / 2;            float treal, timag, ureal, uimag, arg;            int m, k, j, t, index1, index2; 

16、0;          bitrp(xreal, ximag, n);            / 計算 1 的前 n / 2 個 n 次方根的共軛復數(shù) W'j = wreal j + i * wimag j , j = 0, 1, . , n / 2 - 1           

17、arg = (float)(-2 * Math.PI / n);            treal = (float)Math.Cos(arg);            timag = (float)Math.Sin(arg);            wreal0 =

18、1.0f;            wimag0 = 0.0f;            for (j = 1; j < n / 2; j+)                    

19、60;       wrealj = wrealj - 1 * treal - wimagj - 1 * timag;                wimagj = wrealj - 1 * timag + wimagj - 1 * treal;            

20、0;           for (m = 2; m <= n; m *= 2)                            for (k = 0; k < n; k += m)   &#

21、160;                                for (j = 0; j < m / 2; j+)              &

22、#160;                             index1 = k + j;                   &#

23、160;    index2 = index1 + m / 2;                        t = n * j / m;    / 旋轉(zhuǎn)因子 w 的實部在 wreal 中的下標為 t         

24、               treal = wrealt * xrealindex2 - wimagt * ximagindex2;                        timag = wrealt * ximagin

25、dex2 + wimagt * xrealindex2;                        ureal = xrealindex1;                   

26、;     uimag = ximagindex1;                        xrealindex1 = ureal + treal;              

27、60;         ximagindex1 = uimag + timag;                        xrealindex2 = ureal - treal;         

28、;               ximagindex2 = uimag - timag;                                

29、;                            return n;                public static int IFFT(float xreal, float ximag)

30、60;                   /n值為2的N次方            int n = 2;            while (n <= xreal.Length)  

31、                          n *= 2;                        n /= 2; 

32、           / 快速傅立葉逆變換            float wreal = new floatn / 2;            float wimag = new floatn / 2;      &

33、#160;     float treal, timag, ureal, uimag, arg;            int m, k, j, t, index1, index2;            bitrp(xreal, ximag, n);       &#

34、160;    / 計算 1 的前 n / 2 個 n 次方根 Wj = wreal j + i * wimag j , j = 0, 1, . , n / 2 - 1            arg = (float)(2 * Math.PI / n);            treal = (float)(Math.Cos(arg); 

35、           timag = (float)(Math.Sin(arg);            wreal0 = 1.0f;            wimag0 = 0.0f;        

36、;    for (j = 1; j < n / 2; j+)                            wrealj = wrealj - 1 * treal - wimagj - 1 * timag;       &#

37、160;        wimagj = wrealj - 1 * timag + wimagj - 1 * treal;                        for (m = 2; m <= n; m *= 2)      

38、0;                     for (k = 0; k < n; k += m)                          &#

39、160;         for (j = 0; j < m / 2; j+)                                     &

40、#160;      index1 = k + j;                        index2 = index1 + m / 2;              &#

41、160;         t = n * j / m;    / 旋轉(zhuǎn)因子 w 的實部在 wreal 中的下標為 t                        treal = wrealt * xrealindex2 - wimagt * ximagind

42、ex2;                        timag = wrealt * ximagindex2 + wimagt * xrealindex2;                 

43、60;      ureal = xrealindex1;                        uimag = ximagindex1;              

44、60;         xrealindex1 = ureal + treal;                        ximagindex1 = uimag + timag;         

45、;               xrealindex2 = ureal - treal;                        ximagindex2 = uimag - timag;   &

46、#160;                                                   

47、0;    for (j = 0; j < n; j+)                            xrealj /= n;              

48、  ximagj /= n;                        return n;            這里只給出了函數(shù)FFT()的，函數(shù)IFFT()可以進行相應測試。測試代碼：namespace ConsoleApplication1 

49、0;  class Program            static void Main(string args)                    float a =                 0.5751f,0.4514f,0.0439f,