code: def ndtr(a):
      
      sqrth = math.sqrt(2) / 2
      x = float(a) * sqrth
      z = abs(x)
      if z < sqrth:
          y = 0.5 + 0.5 * math.erf(x)
      else:
          y = 0.5 * math.erfc(z)
          if x > 0:
              y = 1 - y
      return y
docs: Returns the area under the Gaussian probability density function,
      integrated from minus infinity to x.
  
      See: https://docs.scipy.org/doc/scipy/reference/generated/scipy.special.ndtr.html#scipy.special.ndtr