MIMOI ss2tf, how to apply input to TF?

I have a system with 2 inputs and 2 outputs in the form of a state space model in simulink. i want to be able to represent cross coupling in the system by generating 4 transfer functions. However when using "ss2tf(A,B,C,D,iu)" i am only able to use "iu" values of 1 or 2. So how do i generate four tf's?

Next i want to apply a step input to TF11 (the transfer function representing relationship between input 1 and output1) and with nothing appplied to TF22 i want to be able to plot/observe the output at y1 and y2. How do i do this?

Do i need to get differential eqn of TF in order to apply an input to it?

I am very new to matlab so step by step help would be much appreciated (inc any codes that might be useful).

Thanks

Answer 1

[Arkadiy Turevskiy]

Assuming you have your variables a,b,c,d defined in MATLAB workspace, so that

>>size(ss(a,b,c,d))

returns:

State-space model with 2 outputs, 2 inputs, and n states.

(where n is the number of states you have), all you need to do is this:

>>sys=ss(a,b,c,d); % create a 2*2 ss system

>>systf=tf(sys); convert to a 2x2 transfer function

>>step(systf(1,1)); % compute and plot step response of output 1 to input 1

>>step(systf(2,1)); % compute and plot step response of output 2 to input 1

Or, if you do not like to type:

>> step(tf(ss(a,b(:,1),c,d(:,1))))

[ken thompson]

Thank you very much, very helpful.

[fariba]

thank you dear arkadiy turevskiy.your answer was helpful for me.