已知某系统传递函数G，可以调用改代码对系统进行降阶处理。功能同routh降阶相似，不过这里的分子阶次r和分母阶次k可以不止相差1。-Known transfer function of a system G, can call the code to deal with reduced-order system. Routh Reduction with similar features, but here the molecular order r and the denominator or