Plotting Discrete Time Functions

I need to plot 5 cos(π n /6 - π/2) as a discrete tim signal. But I am not getting the proper result.

n = [-5:0.001:5];
y = 5*cos(pi*(n/2)-(pi/2)); 
stem(n,y);

What am I missing from this code to get the discrete time signals?

Answer 1

[Austin Holmes]

The original poster asked for the discrete time signal not the continuous time signal. A discrete time signal just means sampling your continuous signal at discrete time intervals.

The simplest way this can be done is by increasing your step in n.

n = [-5:0.25:5];
y = 5*cos(pi*(n/2)-(pi/2)); 
stem(n,y);

The proper way to do this would be determining a sampling rate and implementing it in your code.

Answer 2

[Freedom TSOKPO]

I've just began with Matlab and I don't even know the function stem.

But I think this code can do it

clear all; clc;

n = -5:0.001:5;

y = 5*cos((n-1)*pi/2); %5*cos(pi*(n/2)-(pi/2));

figure

% axis([-6 6 -4 4]);

plot(n,y);

Answer 3

[Satyam]

t = -1:0.01:1;

impulse_continuous = @(t) t == 0;

unit_step_continuous = @(t) t >= 0;

unit_ramp_continuous = @(t) t .* (t >= 0);

exponential_continuous = @(t) exp(t);

sine_continuous = @(t) sin(2*pi*t);

cosine_continuous = @(t) cos(2*pi*t);

n = -10:10;

impulse_discrete = @(n) n == 0;

unit_step_discrete = @(n) n >= 0;

unit_ramp_discrete = @(n) n .* (n >= 0);

exponential_discrete = @(n) exp(n/10);

sine_discrete = @(n) sin(2*pi*n/10);

% Discrete Cosine Function

cosine_discrete = @(n) cos(2*pi*n/10);

% Plot Continuous Functions

figure;

subplot(3,2,1);

plot(t, impulse_continuous(t), 'LineWidth', 2);

title('Continuous Impulse Function');

xlabel('Time (t)');

ylabel('\delta(t)');

axis([-1 1 -0.5 1.5]);

grid on;

subplot(3,2,2);

plot(t, unit_step_continuous(t), 'LineWidth', 2);

title('Continuous Unit Step Function');

xlabel('Time (t)');

ylabel('u(t)');

axis([-1 1 -0.5 1.5]);

grid on;

subplot(3,2,3);

plot(t, unit_ramp_continuous(t), 'LineWidth', 2);

title('Continuous Unit Ramp Function');

xlabel('Time (t)');

ylabel('r(t)');

axis([-1 1 -0.5 1.5]);

grid on;

subplot(3,2,4);

plot(t, exponential_continuous(t), 'LineWidth', 2);

title('Continuous Exponential Function');

xlabel('Time (t)');

ylabel('e^t');

axis([-1 1 -0.5 3]);

grid on;

subplot(3,2,5);

plot(t, sine_continuous(t), 'LineWidth', 2);

title('Continuous Sine Function');

xlabel('Time (t)');

ylabel('sin(2\pi t)');

axis([-1 1 -1.5 1.5]);

grid on;

subplot(3,2,6);

plot(t, cosine_continuous(t), 'LineWidth', 2);

title('Continuous Cosine Function');

xlabel('Time (t)');

ylabel('cos(2\pi t)');

axis([-1 1 -1.5 1.5]);

grid on;

% Plot Discrete Functions

figure;

subplot(3,2,1);

stem(n, impulse_discrete(n), 'filled');

title('Discrete Impulse Function');

xlabel('n');

ylabel('\delta[n]');

axis([-10 10 -0.5 1.5]);

grid on;

subplot(3,2,2);

stem(n, unit_step_discrete(n), 'filled');

title('Discrete Unit Step Function');

xlabel('n');

ylabel('u[n]');

axis([-10 10 -0.5 1.5]);

grid on;

subplot(3,2,3);

stem(n, unit_ramp_discrete(n), 'filled');

title('Discrete Unit Ramp Function');

xlabel('n');

ylabel('r[n]');

axis([-10 10 -5 15]);

grid on;

subplot(3,2,4);

stem(n, exponential_discrete(n), 'filled');

title('Discrete Exponential Function');

xlabel('n');

ylabel('e^{n/10}');

axis([-10 10 -0.5 3]);

grid on;

subplot(3,2,5);

stem(n, sine_discrete(n), 'filled');

title('Discrete Sine Function');

xlabel('n');

ylabel('sin(2\pi n/10)');

axis([-10 10 -1.5 1.5]);

grid on;

subplot(3,2,6);

stem(n, cosine_discrete(n), 'filled');

title('Discrete Cosine Function');

xlabel('n');

ylabel('cos(2\pi n/10)');

axis([-10 10 -1.5 1.5]);

grid on;