Plotting IIR filter error

I have an IIR filter I am trying to plot, but I am not sure what I am doing wrong here. Can someone please help?

My code:

%% This is a first part of an exercise.

% Here you are implementing the transfer function H(z).

% Pass different values of theta and r to have differnt outcome.

clc; clear all;

%% Part -1 simulation

% initialize r

r = 0.99 ;

%initialize theta

theta = pi/3 ;

% initialize omega vector. Let, ω to start from 0 to pi with % 200 intermediate values.

w = 200 ;

% Now, define z = e^(j*w).

z = exp(1i*w);

% implement H

H = 1./(1 - (2*r*cos(theta)*(z.^-1))+((r^2)*(z.^-2)));

% Now, plot the filter magnitude response in dB scale w.r.t w.

figure;plot(w, );grid on;

xlabel('normalized frequency'); ylabel('amplitude in dB')

title('Frequency and phase response at r = and theta = ');

[Star Strider]

What result are you supposed to get, and what result are you getting?

[Nathan Jaqua]

I have not even been able to get anything to show up in the plot. I need it to plot properly.

Answer 1

[Star Strider]

You are plotting one point, so you need to plot a marker instead of a line.

I am not certain what you are doing, so consider this example:

% Now, define z = e^(j*w).
z = @(w) exp(1i*w);
 
% implement H
H = @(w) 1./(1 - (2*r*cos(theta)*(z(w).^-1))+((r^2)*(z(w).^-2)));
 
% Now, plot the filter magnitude response in dB scale w.r.t w.  
w = linspace(-100*pi, 100*pi, 250);
figure;plot(w, abs(H(w)));grid on;
xlabel('normalized frequency'); ylabel('amplitude in dB')
title('Frequency and phase response at r = and theta = ');

Experiment to get the result you want.