Compute the product set of array_a and array_b and sort it.

def sorted_product_set(array_a, array_b):
  """Compute the product set of array_a and array_b and sort it."""
  return np.sort(
      np.concatenate(
          [array_a[i] * array_b for i in xrange(len(array_a))], axis=0)
  )[::-1]