Negative Values in Step Response

on 26 May 2013

Azzi Abdelmalek (view profile)

Hi guys,

I just noticed something interesting on MATLAB.

I was working with a transfer function, and I inserted a delay using a Pade approximation, and plotted the step response. At first glance, it seems just like any other step response, however when i zoomed in on the origin, I noticed that it slightly dips into negative values before coming up.

I've never noticed this before. Anyone have any idea why it does this?

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Azzi Abdelmalek (view profile)

on 26 May 2013

This is normal, when your transfer function contains positives zeros

example H(p)=(-p+2)/(p^2+2p+1)

```step([-1 2],[1 2 1])
```

Kenneth

Kenneth (view profile)

on 26 May 2013

Hmm indeed it did have a positive zero. Why does it do this though? What does it mean?

Rajiv Singh

on 26 May 2013
Kenneth

Kenneth (view profile)

on 26 May 2013

Interesting stuff, thanks for the info!

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