写论文的时候由于需要画出系统的零极点图。但是之前不知道怎么用matlab画，今天研究了一下，拿出来和大家共享。所用到的matlab函数为zplane，matlab给出的解释如下：

     ZPLANE Z-plane zero-pole plot.
    ZPLANE(Z,P) plots the zeros Z and poles P (in column vectors) with the
    unit circle for reference.  Each zero is represented with a ''o'' and
    each pole with a ''x'' on the plot.  Multiple zeros and poles are
    indicated by the multiplicity number shown to the upper right of the
    zero or pole.  ZPLANE(Z,P) where Z and/or P is a matrix, plots the zeros
    or poles in different columns using the colors specified by the axes
    ColorOrder property.
 
    ZPLANE(B,A) where B and A are row vectors containing transfer function
    polynomial coefficients plots the poles and zeros of B(z)/A(z).  Note
    that if B and A are both scalars they will be interpreted as Z and P.
 
    [HZ,HP,Hl] = ZPLANE(Z,P) returns vectors of handles to the lines and
    text objects generated.  HZ is a vector of handles to the zeros lines,
    HP is a vector of handles to the poles lines, and Hl is a vector of
    handles to the axes / unit circle line and to text objects which are
    present when there are multiple zeros or poles.  In case there are no
    zeros or no poles, HZ or HP is set to the empty matrix [].
 
    ZPLANE(Z,P,AX) puts the plot into the axes specified by the handle AX.

      假设为一个零点，多个极点系统且b=[0.2 0.8 0.64],a=1,用zplane（b,a）就可以画出如下的系统零极点图。