code: def convertStateToIndex(population, fire):
      
      assert 0 <= population < POPULATION_CLASSES, "'population' must be in " \
          "(0, 1...%s)" % str(POPULATION_CLASSES - 1)
      assert 0 <= fire < FIRE_CLASSES, "'fire' must be in " \
          "(0, 1...%s) " % str(FIRE_CLASSES - 1)
      return(population * FIRE_CLASSES + fire)
docs: Convert state parameters to transition probability matrix index.
      
      Parameters
      ----------
      population : int
          The population abundance class of the threatened species.
      fire : int
          The time in years since last fire.
      
      Returns
      -------
      index : int
          The index into the transition probability matrix that corresponds to
          the state parameters.