def get_fitness (self, feature_set):
        ## NB: override this fitness function
        return 1.0 - abs(sum(feature_set) - self.target) / float(self.target)
determine the fitness ranging [0.0, 1.0]; higher is better
dataset/ETHPy150Open ceteri/exelixi/src/uow.py/UnitOfWorkFactory.get_fitness