1    package math.transforms.fft; 
2     
3    //Title:        1-d mixed radix Inverse FFT. 
4    //Version: 
5    //Copyright:    Copyright (c) 1998 
6    //Author:       Dongyan Wang 
7    //Company:      University of Wisconsin-Milwaukee. 
8    //Description: 
9    //              According to the definition of the inverse fourier transform, 
10   //              We can use FFT to calculate the IFFT, 
11   //                 IFFT(x) = 1/N * conj(FFT(conj(x)). 
12   // 
13   //              . Change the sign of the imaginary part of the FFT input. 
14   //              . Calculate the FFT. 
15   //              . Change the sign of the imaginary part of the FFT output. 
16   //              . Scale the output by 1/N. 
17   // 
18    
19    
20   public class IFFT1d { 
21     int N; 
22    
23     // Constructor: IFFT of Complex data. 
24     public IFFT1d(int N) { 
25       this.N = N; 
26     } 
27    
28     public void ifft(float inputRe[], float inputIm[]) { 
29    
30   //  Change the sign of the imaginary part of the FFT input. 
31       for (int i = 0; i < N; i++) 
32         inputIm[i] = -inputIm[i]; 
33    
34   //  Calculate the FFT. 
35       FFT1d fft1 = new FFT1d(N); 
36       fft1.fft(inputRe, inputIm); 
37    
38   //  Change the sign of the imaginary part of the FFT output. 
39   //  Scale output by 1/N. 
40    
41       for (int i = 0; i < inputRe.length; i++) { 
42         inputRe[i] = inputRe[i] / N; 
43         inputIm[i] = -inputIm[i] / N; 
44       } 
45     } 
46   } 
47