code: public void inverse (double data[], int i0, int stride) {
      backtransform(data, i0, stride);
  
    /* normalize inverse fft with 1/n */
      double norm = normalization();
      for (int i = 0; i < n; i++) {
        data[i0+stride*i]   *= norm;
        data[i0+stride*i+1] *= norm; }}
docs: Compute the (nomalized) inverse FFT of data, leaving it in place.
  The frequency domain data must be in wrap-around order, and be stored
  in the following locations:
  <PRE>
  Re(D[i]) = data[i0 + stride*i]
  Im(D[i]) = data[i0 + stride*i+1]
  </PRE>