# Can I cascade (multiply) transfer functions in MATLAB?

You can multiply transfer functions sys1=tf(num1,den1) and sys2 = tf(num2, den2) using sys3=sys1*sys2. you can also add them, subtract them, etc. if you want you can also use feedback(sys1,sys2) which finds the result of the feedback loop where sys1 is the transfer function going forward on the top half of the loop, and sys2 is the bottom half transfer function going backward in the loop. this is equivalent to sys1/(1+sys1*sys2), the closed-loop transfer function. Note: be careful of signs when you are using positive feedback instead of negative feedback, the 'feedback' command assumes negative feedback.

For instance, in Problem 2 (d), you can use these techniques to calculate the closed loop transfer function Hyr if you have all of the intermediate transfer functions entered into MATLAB.

--Fuller 15:45, 12 November 2007 (PST)