One of the powers of SIMULINK is the ability to construct block diagrams that provide an intuitive approach to simulating feedback-control systems. Often we use linear transfer functions to simulate the behavior of linear systems. A block titled “sfun” can obtained from the “nonlinear” library in SIMULINK and placed in a SIMULINK diagram. When simulations are performed, the equations in the sfun m-file are solved simultaneously with other blocks in the block diagram. The sfun file must be given a name with a '.m' extension, while the block diagram is given a '.mdl' extension.