def clip_nn_log_std(log_std, _min=-20, _max=2):
    """
    scale log_std from [-1, 1] to [_min, _max]
    Args:
        log_std: log standard deviation of a gaussian distribution
        _min: corrected minimum
        _max: corrected maximum
    Return:
        log_std after scaling, range from _min to _max
    """
    return _min + 0.5 * (_max - _min) * (log_std + 1)