Elements and constructs of a signal flow graph. a) a node labeled x, b) a branch with a multiplicative gain of m, c) a branch with a multiplicative gain of one, d) an input node labeled Vin with an optional multiplicative gain of m, e) an output node labeled Iout with an optional multiplicative gain of m. f) addition, g) a loop with a loop gain of Am, h) a complex expression Z = c( aX + bY ).