<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def mean_min_time_distance(item_a, item_b, max_value):
 """ Calculate the mean time difference among the time steps in each object. Args: item_a: STObject from the first set in TrackMatcher item_b: STObject from the second set in TrackMatcher max_value: Maximum distance value used as scaling value and upper constraint. Returns: Distance value between 0 and 1. """

    times_a = item_a.times.reshape((item_a.times.size, 1))
    times_b = item_b.times.reshape((1, item_b.times.size))
    distance_matrix = (times_a - times_b) ** 2
    mean_min_distances = np.sqrt(distance_matrix.min(axis=0).mean() + distance_matrix.min(axis=1).mean())
    return np.minimum(mean_min_distances, max_value) / float(max_value)