Conversion of an Arbitrary Nonsource Node into a Source Node in the Signal-Flow Graph

Signal-flow graph technique is one of the most versatile methods in the modem analysis of linear networks and systems. This technique was therefore incorporated into a senior course on linear circuits in a Canadian university. Students were, in general, fascinated by the easy manipulation of the variables of interest, but they tended to use Mason's formula even when it was not applicable, e.g., when the desired quantity was the transmission gain from a nonsource node to another node, thus obtaining a wrong answer. Two rules are proposed by which any node, nonsource or sink, in the signal-flow graph can be directly converted to a source node, without rewriting the set of system equations of the original graph. These rules thus make it possible to obtain various quantities, i.e., gains and network functions, through simple graphical manipulations.