def predict(self, kalman_filter):
        """
        Propagate the state distribution to the current time step using a Kalman
        filter prediction step.
        """
        self.mean, self.covariance = kalman_filter.predict(self.mean,
                                                           self.covariance)
        self.age += 1
        self.time_since_update += 1

        Propagate the state distribution to the current time step using a Kalman
        filter prediction step.
        
ppdet/modeling/mot/tracker/base_sde_tracker.py