text: # -*- coding: utf-8 -*-
  
  from numpy import sin
  
  
  def comp_surface_opening(self):
      """Compute the Slot opening surface (by analytical computation).
      Caution, the bottom of the Slot is an Arc
  
      Parameters
      ----------
      self : SlotW13
          A SlotW13 object
  
      Returns
      -------
      S: float
          Slot opening surface [m**2]
  
      """
  
      Rbo = self.get_Rbo()
  
      S1 = self.H0 * self.W0
      H1 = self.get_H1()
      S2 = 0.5 * (self.W0 + self.W1) * H1
  
      # The bottom is an arc
      alpha = self.comp_angle_opening()
      Sarc = (Rbo ** 2.0) / 2.0 * (alpha - sin(alpha))
  
      # Because Slamination = S - Zs * Sslot
      if self.is_outwards():
          return S1 + S2 - Sarc
      else:
          return S1 + S2 + Sarc
  