/*
  Converts the FFTed data in the complex conjugate
*/
static VALUE dvector_fft_conj(VALUE self)
{
  long len;
  double * v1 = Dvector_Data_for_Write(self, &len);
  double * img;
  long i;
  for(i = 1, img = v1 + len-1; i < (len+1)/2;
      i++, img--)
    *img = -*img;
  return self;
}