static double[] shortToDoubleArray(short[] a, int start, int end) {
  double[] b = new[end-start];
  for (int i = start; i < end; i++)
    b[i-start] = a[i];
  ret b;
}

static double[] shortToDoubleArray(short[] a, IntRange r) {
  ret shortToDoubleArray(a, r.start, r.end);
}