Why do my MATLAB plots always begin from zero?

suppose I have the following equation y = cos(n)

to make the discrete plot

figure 
subplot(2,2,1);
n = linespace(-10,10,20);
y = cos(n);
stem(y)
xlabel('blah blah blah')
ylabel('y[n]')
title('blah')
grid on

When I save the above code in a MATLAB scipt and run it in MATLAB, my graphs always begin from zero, even when I explicitly specify in the the beginning endpoint be negative linspace(-10,10,50)

Why does it do this?

Answer 1

[Star Strider]

The begin and end wherever you tell them to.

Change your stem call to:

stem(n,y)

and see if that improves your result.

Answer 2

[Image Analyst]

Becuse you're not passing in the "X" values, which you call n. Also, did you know that you can call xlim() to have the axes start and stop wherever you want? Otherwise it tried to pick nice "round" numbers rather than weird fractional numbers. Try this:

n = linspace(-10,10,20);
y = cos(n);
stem(n, y, 'LineWidth', 3)
xlabel('n')
ylabel('cos(n)')
title('Stem of cos()')
grid on;
xlim([min(n), max(n)]);