docs: def run_friedman_smooth(x, y, span):
      """Run the FORTRAN smoother."""
      N = len(x)
      weight = numpy.ones(N)
      results = numpy.zeros(N)
      residuals = numpy.zeros(N)
      mace.smooth(x, y, weight, span, 1, 1e-7, results, residuals)
      return results, residuals