zpk2tf Zero pole gain to transfer function

## Syntax

    S = zpk2tf(sys)

## Arguments

sys

  A linear dynamical system in zero-pole-gain representation (see zpk).

S

  The rational transfer function representation of sys.

## Description

Converts a zero pole gain representation to rational transfer function

## Examples

    sys = zpk([2;1], [0;-3-%i;-3+%i], 2.5, "c")
    typeof(sys)

    S = zpk2tf(sys)
    typeof(S)

    --> sys = zpk([2;1], [0;-3-%i;-3+%i], 2.5, "c")
     sys  =
            (s-2) (s-1)
       2.5 -------------
           s (s^2+6s+10)

    --> typeof(sys)
     ans  =
      "zpk"

    --> S = zpk2tf(sys)
     S  =

       5 -7.5s +2.5s²
       --------------
        10s +6s² +s³

    --> typeof(S)
     ans  =
      "rational"

## See Also

- zp2tf
- zpk2ss

## History

6.0

Function added.