Where: g (s)-the total transfer function of the system; N- is the number of forward channels; ρ κ-the transfer function of the k-th forward path, and the signal path from the input end to the output end is called the forward path; △—— The characteristic formula of the flow chart△ =1-σ li+σ ljlk-σ liljlk.

Where li-is the sum of transfer functions of all different circuits; Ljlk-the sum of the products of all non-contact circuits (note: three non-contact circuits do not mean non-contact); LiJLK- the sum of the products of the transfer functions of all three non-contact circuits; △κ-cofactor of the characteristic formula of the k-th forward path, that is, the characteristic formula of the flow chart will contact the loop of the k-th forward path.

Replace the transfer function with zero, and the rest is △κ. The loop transfer function refers to the product of the forward channel and the feedback channel transfer function of the feedback loop, including the positive and negative signs of the feedback polarity.