Negative exponent and reverse order in MuPad

Hello there,

I want to have a polynomial with negative power of the main variable. something like the one below:

f(z)=a0+a1*z^(-1)+...+an*z^(-n).

And I want the reverse order of z power to be held if there is any math operation applied to this expression.

At the moment, MuPad shows negative powers as fractional expressions and also doesn't hold order for me.

Please help.