ztrans_discrete

  ZTRANS_DISCRETE Evaluate the discrete Z transform for a value of z

   OUT = ZTRANS_DISCRETE(N, V, Z)

   Given an array of sample locations N and an array of
   corresponding values V, computes the Z-transform and evaluates
   the result at Z.  Z can be an array.

   The Z-transform is

      X(Z) = sum{all_N}{V(n)*z^(-n)}