With the selected log_probs for multi-discrete actions of behaviour
    and target policies we compute the log_rhos for calculating the vtrace.

def get_log_rhos(target_action_log_probs, behaviour_action_log_probs):
    """With the selected log_probs for multi-discrete actions of behaviour
    and target policies we compute the log_rhos for calculating the vtrace."""
    t = tf.stack(target_action_log_probs)
    b = tf.stack(behaviour_action_log_probs)
    log_rhos = tf.reduce_sum(t - b, axis=0)
    return log_rhos