ZPLANE ZPLANE Zero-pole plot

Usage

 This function makes a zero-pole plot of a discrete-time
 system defined by its zeros and poles. The various syntaxes
 are

    zplane(z,p)

 where z and p are the zeros and the poles of the system
 stored as column vectors, or

    zplane(b,a)

 where a and b are the polynomial coefficients of the
 numerator and denominator stored as line vectors (roots is
 used to find the zeros and poles). The symbol 'o' represents
 a zero and the symbol 'x' represents a pole. The plot includes
 the unit circle for reference.
Contributed by Paulo Xavier Candeias under GPL
