def get_L_star(tasks):
    """
    Get the L* value for the given periodic task set.

    Parameters
    ----------
    tasks : list of pSyCH.task.Periodic
        Set of periodic tasks, for which the L* value needs to be computed.

    Returns
    -------
    float
        L* value for the task set.

    """
    L = 0
    U = 0
    for task in tasks:
        u = task.c/task.t
        L += (task.t - task.d)*u
        U += u
    L /= (1-U)
    return round(L, 3)