# getting error while using feedback

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bhanu kiran vandrangi 2021년 8월 5일
댓글: bhanu kiran vandrangi 2021년 8월 6일
syms s d e
y=((0.005659*s^2+0.05206*s+0.004496)/(s^3+9.357*s^2+2.228*s+0.06147))*((27.5084*d)+(27.5084*(e/s)))
using feedback(y,1,-1) is giving me a error, what is wrong here

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### 답변(3개)

Jesús Zambrano 2021년 8월 5일
You need to work with model objects, they must be either continuous os discrete with identical sample times.
Hope it helps!
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bhanu kiran vandrangi 2021년 8월 6일
ok, but if my input for feedback is matrix then how to use feedback in matlab

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Paul 2021년 8월 5일
The Control System Toolbox does not support operations on sym objects. Having siad that, the error message that I'm seeing is fairly opaque, something about "not enough input arguments," which isn't very helpful.
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VBBV 2021년 8월 5일
```%if true
K1 = tf([0.005659 0.05206 0.004496],[1 9.357 2.228 0.06147])
K2 = tf([0 0 27.5084 0],[0 0 27.5084 0])
feedback(K1,K2,1)
```

Try something like above. Split the function to two TF and apply feedback

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Paul 2021년 8월 5일
Wow. When I read read the question, it never occured to me that e and d are signals, as opposed to unquantifed parameters. Having said that I think that K2 should be:
K2 = tf(27.5084,[1 0]);
And K2 should be in the forward path, not the feedback path? And sitll need to account for the disturbance input, d.

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R2020b

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