High Quality Content by WIKIPEDIA articles! A signal-flow graph (SFG) is a special type of block diagram—and directed graph—consisting of nodes and branches. Its nodes are the variables of a set of linear algebraic relations. An SFG can only represent multiplications and additions. Multiplications are represented by the weights of the branches; additions are represented by multiple branches going into one node. A signal-flow graph has a one-to-one relationship with a system of linear equations. In addition to this, it can also be used to represent the signal flow in a physical system; i.e., it can represent relations of cause and effect.