code: def create_aeff(event_class, event_type, egy, cth):
      
      irf = create_irf(event_class, event_type)
      irf.aeff().setPhiDependence(False)
      theta = np.degrees(np.arccos(cth))
  
      # Exposure Matrix
      # Dimensions are Etrue and incidence angle
      m = np.zeros((len(egy), len(cth)))
  
      for i, x in enumerate(egy):
          for j, y in enumerate(theta):
              m[i, j] = irf.aeff().value(x, y, 0.0)
  
      return m
docs: Create an array of effective areas versus energy and incidence
      angle.  Binning in energy and incidence angle is controlled with
      the egy and cth input parameters.
  
      Parameters
      ----------
      event_class : str
          Event class string (e.g. P8R2_SOURCE_V6).
  
      event_type : list
  
      egy : array_like
          Evaluation points in energy (MeV).
  
      cth : array_like
          Evaluation points in cosine of the incidence angle.