text: import numpy as np
  
  from compressible_tools import *
  
  class Diffuser:
      """A ramjet diffuser. Assumed isentropic with choked throat.
  
      Parameters
      ----------
      T_inf : float
          Freestream temperature.
  
      p_inf : float
          Freestream pressure.
  
      V_inf : float
          Freestream velocity.
  
      gas : Species
          Instance of Species describing the gas in the diffuser.
  
      d_inlet : float
          Diameter of diffuser inlet.
  
      d_exit : float
          Diameter of diffuser exit.
      """
  
      def __init__(self, T_inf, p_inf, V_inf, gas, d_inlet, d_exit):
  
          # Store
          self.T_inf = T_inf
          self.p_inf = p_inf
          self.V_inf = V_inf
          self.gas = gas
          self.d_inlet = d_inlet
          self.d_exit = d_exit
  
          # Calculate inlet parameters
          self.c_inf = np.sqrt(self.gas.gamma*self.gas.R_g*self.T_inf)
          self.M_inf = self.V_inf/self.c_inf
  
          # Calculate geometry
          self.A_inlet = 0.25*np.pi*self.d_inlet**2
          self.A_exit = 0.25*np.pi*self.d_exit**2
  
          # Calculate stagnation properties
          self.T0 = self.T_inf*isentropic_temp_ratio(self.M_inf, self.gas.gamma)
          self.P0 = self.p_inf*isentropic_pressure_ratio(self.M_inf, self.gas.gamma)
  
          # Calculate throat temperature
          self.T_throat = self.T0/isentropic_temp_ratio(1.0, self.gas.gamma)
  
          # Calculate sonic area
          area_ratio = A_A_star_of_M(self.M_inf, self.gas.gamma)
          self.A_star = self.A_inlet/area_ratio
  
          # Calculate exit Mach number
          self.M_exit = M_of_A_A_star(self.A_exit/self.A_star, self.gas.gamma, subsonic=True)
  
          # Calculate exit temperature and pressure
          self.T_exit = self.T0/isentropic_temp_ratio(self.M_exit, self.gas.gamma)
          self.p_exit = self.P0/isentropic_pressure_ratio(self.M_exit, self.gas.gamma)
  
          # Calculate exit velocity
          self.c_exit = np.sqrt(self.gas.gamma*self.gas.R_g*self.T_exit)
          self.V_exit = self.M_exit*self.c_exit
  
          # Calculate diffuser massflow
          self.m_dot = self.A_star*self.P0*np.sqrt(self.gas.gamma/(self.T0*self.gas.R_g)*(2.0/(self.gas.gamma+1.0))**((self.gas.gamma+1.0)/(self.gas.gamma-1.0)))