A strange issue in calculating the transfer function

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Yuxing Zhang 2018-11-7

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https://ww2.mathworks.cn/matlabcentral/answers/428583-a-strange-issue-in-calculating-the-transfer-function

编辑： Bolu Faremi 2020-11-2

I have a SISO state space model like below,but the transfer function I get from MATLAB doesn't match my calculation.The adjoint of A should be the last row and last column,so it's s^2(s+1)^3 and make TF to be 1/(s+2), but why my TF shows exactly different thing? Can any one tell me what's wrong with my system?

A=[0 1 0 0 0 0
    0 0 0 0 0 0
    0 0 -1 1 0 0
    0 0 0 -1 1 0
    0 0 0 0 -1 0
    0 0 0 0 0 -2];
B=[0;1;0;0;1;1];
C=[0 0 1 0 0 1];
D=0;
sys = ss(A,B,C,D);
TF=tf(sys) 
TF =
        s^3 + 3 s^2 + 4 s + 3
    -----------------------------
    s^4 + 5 s^3 + 9 s^2 + 7 s + 2

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Answer 1

Yuxing Zhang 2018-11-7

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https://ww2.mathworks.cn/matlabcentral/answers/428583-a-strange-issue-in-calculating-the-transfer-function#answer_345724

I find out the issue, no need to answer this, I just make mistake in calculating the adjoint

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Bolu Faremi 2020-11-2

编辑：Bolu Faremi 2020-11-2

Hi Zhang,

Could you share any links/knowledge on how you got the adjoint of the TF. I have a similar challenge. I need to obtain the adjoint of a closed loop transfer fucntion. I have the TF, but i am stuck on how to obtain the Adjoint.

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