confused abt z and z(-1) in matlab

moonman (view profile)

on 13 Nov 2011
Accepted Answer by Naz

Naz (view profile)

Lets suppose i am having one transfer function as

H(z)= 1-2z/(1+3z)

and the other is

G(z) = 1-2z(-1)/ [1+3z(-1)] //Now inverse is used

If i want to take the transfer fucntion in matlab for further pole zero map, how i will tell matlab that it is z in my TF or z(-1)

Walter Roberson

Walter Roberson (view profile)

on 13 Nov 2011

Is that really z multiplied by negative one? Or is it z raised to the power of negative 1, z^(-1), which is 1/z ?

moonman

moonman (view profile)

on 13 Nov 2011

It is z raise to power -1
yes 1/z...

H(z) contaiins all z

G(z) contains all z(inverse power)

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Naz (view profile)

on 13 Nov 2011

You can take your H(z) and divide by z. So you will have: z^(-1)-2 / z^(-1)+3. Now you can create two vectors containing zeros and poles:

```B=[-2 1];
A=[3 1];
zplane(B,A)
```

If you have function with (all) negative powers, than the last coefficient is for the most negative power and the first coeff is a constant. In case of all positive coeff. you just inverse the order (constant is last).

moonman

on 13 Nov 2011

Thanks Naz

moonman (view profile)

on 13 Nov 2011

Is there any way i can directly use H(z) for calculations

Walter Roberson

Walter Roberson (view profile)

on 13 Nov 2011

Not without the symbolic toolbox.

Naz

Naz (view profile)

on 13 Nov 2011

I dont really understand what you are trying to do. Please, be more specific.

moonman (view profile)

on 13 Nov 2011

I just want to ask that some times we are having transfer function which is expressed in z and some times it is expressed in z(inverse) format

how to handle both I am sure both cannot be handled by one command of matlab like tf is used with z(inverse)

Naz

Naz (view profile)

on 13 Nov 2011

See my answer, I just updated it.

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