How to simplify transfer function？

Question

tqy 2012-4-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/36520-how-to-simplify-transfer-function

评论： Zuhair Abduljabbar 2021-1-31

Hi guys

I have used the function s=tf('s') to ceate a transfer function, but  I find that Matlab do not simplify the tf at all.
for example.
s=tf('s');
A=1/(1+s);B=A/(1+A);
the result is 1+s/(s^2+3*s+2)
What I want is 1/(2+s)

Anyone know that how to simplify the tf in Matlab?

Thank you!

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Answer 1

Thomas 2012-4-25

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/36520-how-to-simplify-transfer-function#answer_45661

在 MATLAB Online 中打开

Try

s=tf('s');
A=1/(1+s);B=A/(1+A);
minreal(B)

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tqy 2012-4-27

Thanks a lot.

But in another case, I have to set the tolerance so that I can get what I want.

I think Matlab only keeps the default effective bit of the a number.

Tim 2015-2-5

在 MATLAB Online 中打开

Looks like a solution to my problem, however I need to find variables from a rewritten tf.

I have a tf G like below

    lsys = ss(A B C D); % were all matrices are 3x3
    G = tf(lsys);
from which I am intersted in rewriting G(2,2)
G(2,2)=
    1.422e-05 s + 4.696e-06
    -----------------------
     s^2 + 21.76 s + 1.216
into
      a * (b*s + 1)
    -----------------
     (c*s +1)*(d*s+1)
to yield constants a b c d
MatLab does not accept 
minreal(G(2,2));