Polynomial Factoring with negative powers

Hello Everybody. My first msg so glad to be here. I am just starting with Matlab so, maybe its a simple question but I didnt found the solution.

I have a polynomial like

D^1+D^-1+ 1

and I want it

(D^1-a1)(D^1-a2)

Sure matlab can do it, but how?

Thank you

Answer 1

[Matt J]

Rewrite as a rational function

 (D^2+D+1)/D

Now use ROOTS to factor the numerator

    >> roots([1,1,1])

    ans =

      -0.5000 + 0.8660i
      -0.5000 - 0.8660i