How to input transfer function without simplifying it?

Supermankid (view profile)

on 12 Sep 2017
Latest activity Answered by Teja Muppirala

Teja Muppirala (view profile)

on 13 Sep 2017
Accepted Answer by Teja Muppirala

Teja Muppirala (view profile)

Hi everyone,
Normally, we can give numerator = [ 1 0]; denominator =[1 1 4]; and system1=tf(num,den); but if the transfer function is like:
G(s) = {s + 2}/{s(s − 1)(s + 6)^2}
can I add this transfer function without simpligying (I mean without multiplying the denominators)
=> only from s(s-1)(s+6)^2
May be someone can provide some tips.

Walter Roberson

Walter Roberson (view profile)

on 12 Sep 2017
G = tf([1 2],[1 0]) * tf(1,[1 -1]) * tf(1, [1 6])^2

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Answer by Teja Muppirala

Teja Muppirala (view profile)

on 13 Sep 2017

s = tf('s')
G = (s+2)/(s*(s-1)*(s+6)^2)
This gives a transfer function (tf) with the polynomials expanded
G =
s + 2
----------------------------
s^4 + 11 s^3 + 24 s^2 - 36 s
Or you can express it as a ZPK (zero-pole-gain)
G = zpk((s+2)/(s*(s-1)*(s+6)^2))
Then you get
G =
(s+2)
---------------
s (s+6)^2 (s-1)