Matlab extract coefficient from z transform function

Question

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Hi I have a z transform function 3/z + 5/z^2 + 6/z^3 + 1

How would I extract the coefficients from this equation? I have tried using coeffs and it says it is not a polynomial.

I would like the answer to come out as [3 5 6 1]

The symbolic z variable is declared as syms z

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Answer 1

Star Strider 2014-5-10

编辑：Star Strider 2014-5-10

0 个投票

Use the sym2poly function, although here it’s necesary to do an intermediate step:

syms z 
fz = 3/z + 5/z^2 + 6/z^3 + 1
[fzn, fzd] = numden(fz)
fzc = sym2poly(fzn)
fzc = circshift(fzc, [0 -1])

produces:

fzc =
       3     5     6     1

David 2014-5-10

Thank you so much for your input. It was exactly what I was looking for.

Star Strider 2014-5-10

My pleasure!

The sym3poly function would work with a ‘normal’ polynomial, but the symbolic terms in the denominator require numden and then circshift.