how to get z-transform expression along with the curve of this function

I am getting the plot for this function. But i want to show the H(z) of this butterworth lowpass filter. Can You pls help me with this!

Answer 1

[Dimitris Kalogiros]

Try this:

clear; clc;

fc=500; %Hz;
fs=2000; %Hz;

n=4; % filter order
[b,a] = butter(n ,fc/(fs/2));

freqz(b,a);

You should get:

[Gaurav Sharma]

sorry man but it didnt work. But anyway, I figured it out: use filt(b,a) you will get the z trans. expression