ZFresp:

------------------------------------------------------------------------
   Generates the frequency response for a digital filter.

                       -1               -nb
           b(1) + b(2)z   + � + b(nb+1)z
   H(z) = ---------------------------------
                       -1               -na
           a(1) + a(2)z   + � + a(na+1)z

   The routine interprets your input as follows:
   If only 2 arguments are input it computes the frequency response
   for 0 to � at 512 points.

   If 3 arguments are entered and the third is a scalar it will
   interpret n as follows:

     if ( n > 2� ),
       do n point response between 0 and �
       else if ( n < 2� ),
         if n is an integer do an n point response between 0 and �
       else
         treat n as a scalar frequency
       end
     end

     if 4 arguments are entered it will do an n point response between
     0 and 2�.
------------------------------------------------------------------------
   Form:
   [h, w] = ZFresp( num, den, n, rnge )
------------------------------------------------------------------------

   ------
   Inputs
   ------
   num                 Numerator polynomial
   den                 Denominator polynomial
   n                   Number of points
   rnge                Range (text)           

   -------
   Outputs
   -------
   h                   Complex output vector
   w                   Frequency points 

------------------------------------------------------------------------

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