Decorator over JTransforms for computing FFTs in NumPy fashion in Java

FFT.java

import edu.emory.mathcs.jtransforms.fft.DoubleFFT_1D;

/**
 * Wrapper class over JTransforms library for fourier transforms.
 * @author apurv
 *
 */
public class FFT {

  public static Complex[] fft1D(Complex[] signal){
    int n = signal.length;
    Complex[] fourier = new Complex[n];
    
    double[] coeff = new double[2*n];
    int i = 0;
    for(Complex c:signal){
      coeff[i++] = c.getReal();
      coeff[i++] = c.getImaginary(); 
    }
    
    DoubleFFT_1D fft = new DoubleFFT_1D(n);
    fft.complexForward(coeff);
    
    for(i = 0; i < 2*n; i+=2){
      Complex c    = new Complex(coeff[i], coeff[i+1]);
      fourier[i/2] = c;
    }    
    return fourier;
  }
  
  
  public static Complex[] fftShift1D(Complex[] fTransform){
    int n   = fTransform.length;
    int mid = (n-1)/2;
    Complex[] shift = new Complex[n];
    int j = 0;
    for(int i = mid+1; i < n; i++){
      shift[j] = fTransform[i];
      j++;
    }
    
    for(int i = 0; i <= mid; i++){
      shift[j] = fTransform[i];
      j++;
    }
    return shift;
  }
  
  public static Complex[] ifft1D(Complex[] fourier){
    int n    = fourier.length;
    double s = 1.0 / (double) n;
    
    Complex[] signal = new Complex[n];
    double[] coeff   = new double[2*n];
    
    int i = 0;
    for(Complex c:fourier){
      coeff[i++] = c.getReal();
      coeff[i++] = c.getImaginary(); 
    }
    
    DoubleFFT_1D fft = new DoubleFFT_1D(n);
    fft.complexInverse(coeff, false);
    
    for(i = 0; i < 2*n; i+=2){
      Complex c    = new Complex(s*coeff[i], s*coeff[i+1]);
      signal[i/2] = c;
    }
    return signal;
  }
  
  
  public static Complex[] ifftShift1D(Complex[] fourier){
    int n   = fourier.length;
    int mid = n/2;
    Complex[] shift = new Complex[n];
    int j = 0;
    for(int i = mid; i < n; i++){
      shift[j] = fourier[i];
      j++;
    }
    
    for(int i = 0; i < mid; i++){
      shift[j] = fourier[i];
      j++;
    }
    return shift;    
  }
}