Nyquist Stability Criterion
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1 闭环/开环 零极点关系
符号定义 

G(s) := \frac{N_G(s)}{D_G(s)} , H(s) := \frac{N_H(s)}{D_H(s)}

计算如下表达式： 

\boxed{
\begin{aligned}
G(s)H(s) &= \frac{N_G(s) N_H(s)}{D_G(s) D_H(s)}, \\
1 + G(s)H(s) &= \frac{D_G(s) D_H(s) + N_G(s) N_H(s)}{D_G(s) D_H(s)},\\
\frac{G(s)}{1+G(s)H(s)} &= \frac{N_G(s) D_H(s)}{D_G(s) D_H(s) + N_G(s) N_H(s)}
\end{aligned}
}

发现有如下关系 

P(1+GH) = P(GH...