code: def _h13_s(s):
      
      # Check input parameters
      if s < 3.397782955 or s > 3.77828134:
          raise NotImplementedError("Incoming out of bound")
  
      sigma = s/3.8
      I = [0, 1, 1, 3, 5, 6]
      J = [0, -2, 2, -12, -4, -3]
      n = [0.913965547600543, -0.430944856041991e-4, 0.603235694765419e2,
           0.117518273082168e-17, 0.220000904781292, -0.690815545851641e2]
  
      suma = 0
      for i, j, ni in zip(I, J, n):
          suma += ni * (sigma-0.884)**i * (sigma-0.864)**j
      return 1700 * suma
docs: Define the boundary between Region 1 and 3, h=f(s)
  
      Parameters
      ----------
      s : float
          Specific entropy, [kJ/kgK]
  
      Returns
      -------
      h : float
          Specific enthalpy, [kJ/kg]
  
      Notes
      ------
      Raise :class:`NotImplementedError` if input isn't in limit:
  
          * s(100MPa,623.15K) ≤ s ≤ s'(623.15K)
  
      References
      ----------
      IAPWS, Revised Supplementary Release on Backward Equations p(h,s) for
      Region 3, Equations as a Function of h and s for the Region Boundaries, and
      an Equation Tsat(h,s) for Region 4 of the IAPWS Industrial Formulation 1997
      for the Thermodynamic Properties of Water and Steam,
      http://www.iapws.org/relguide/Supp-phs3-2014.pdf. Eq 7
  
      Examples
      --------
      >>> _h13_s(3.7)
      1632.525047
      >>> _h13_s(3.5)
      1566.104611