code: public double[] toWraparoundOrder(double data[], int i0, int stride) {
      if ((i0==0)&&(stride==2)) return data;
      double newdata[] = new double[2*n];
      for(int i=0; i<n; i++){
        newdata[2*i]   = data[i0+stride*i];
        newdata[2*i+1] = data[i0+stride*i+1]; }
      return newdata; }
docs: Return data in wraparound order.
  i0 and stride are used to traverse data; the new array is in
  packed (i0=0, stride=2) format.
  @see <a href="package-summary.html#wraparound">wraparound format</A>