Mason's rule

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Mason's rule, or the Gain formula is a method of solving for the transfer function of a given control output. It is used frequently in Control theory. It can be determined by looking at a Signal-flow graph, or a Block diagram. The gain formula is as follows:

M = \frac{y_{out}}{y_{in}} = \sum_{k=1}^N \frac{M_k \Delta\ _k}{ \Delta\ }

where:

  • yin = input-node variable.
  • yout = output-node variable
  • M = gain between yin and yout
  • N = total number of forward paths between yin and yout
  • Mk = gain of the kth forward path between yin and yout
  • Δ = 1 - (the sum of the gains of every individual loop) + (the sum of the products of the gains of all possible combinations of two non-touching loops) - (the sum of the products of the gains of all possible combinations of three non-touching loops) + ... and so on and so forth.
  • Pmr = the gain product of the mth possible combination of r non-touching loops (1 ≤ r ≤ N ) (Two parts of a signal-flow graph are non-touching if they do not share a common node)