The stability of Caputo fractional order switching systems is studied in the article by Wu C. etc (Wu and Liu (2019)). The authors claim that the lower bound of the Caputo fractional order derivative needs to be updated at each switching instant. However, the lower bound is relevant to the initial condition and reflects the historical information of a fractional system. No historical information can be changed by subsequent control input as all physical systems are causal systems. The model in Wu and Liu (2019) is physically unattainable and the theoretical achievements cannot be applied in engineering.

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关于“李雅普诺夫和Caputo分数阶切换系统的外部稳定性”的评论

Wu C.等人在论文中研究了Caputo分数阶切换系统的稳定性（Wu and Liu（2019））。作者声称，Caputo分数阶导数的下限需要在每个切换瞬间进行更新。但是，下限与初始条件有关，并且反映了分数系统的历史信息。由于所有物理系统都是因果系统，因此无法通过后续控制输入来更改历史信息。Wu and Liu（2019）中的模型在物理上是无法实现的，理论上的成果无法应用于工程中。