ODE15s可以处理刚性微分方程。采用向后微分公式，效率不是很高，但是对于一些ODE45会失效或计算效果很差的情况下，可以使用。可能是由于方程刚性引起的。(ODE15s can handle rigid differential equations. Using the backward differential formula, the efficiency is not very high, but it can be used when some ODE45 will fail or the calculation results are very poor. It may be caused by the rigidity of the equation.)