I can't see the cosine graph. How do I generate the cosine graph using 2^10 samples?

deltat=0.1;
nsamples=2^10;
time=[0 : deltat : deltat*(nsamples-1)];
for i=1: nsamples
ydata(i,:)=[5+10*cos(2*pi*time+pi/6)];
end


figure(1);
plot(time,ydata,'b')

I try to generate the cosine graph with 2^10 samples.

I used 1024 (=2^10) time samples to create the cosine graph.

The time interval is 0.1 seconds.

Could you explain why I have 1024*1024 ydata rather than 1*1024 ydata?

How do I create a cosine graph using time sample data?

Answer 1

[Voss]

for i=1: nsamples

ydata(i,:)=[5+10*cos(2*pi*time+pi/6)];

end

That calculates 5+10*cos(2*pi*time+pi/6) and assigns it to the first row of ydata, then calculates the same thing again and assigns it to the second row of ydata, etc., etc., for nsamples rows. At the end ydata is a matrix where each row is the same and each row contains the calculated signal for all times.

What you mean to do is simpler than that; just calculate ydata once:

deltat = 0.1;
nsamples = 2^10;
time = (0 : nsamples-1) * deltat;
ydata = 5+10*cos(2*pi*time+pi/6);

figure(1);
plot(time,ydata,'b')

% zooming in
figure
plot(time,ydata,'b')
xlim([0 10])

Answer 2

[Mitchell Thurston]

You should be able to just get rid of the for loop,

ydata = 5 + 10*cos(2*pi*time+pi/6)

Answer 3

[Sam Chak]

deltat      = 0.001;
nsamples    = 2000;
time        =[0 : deltat : deltat*(nsamples-1)];
size(time)

ans = 1x2

1 2000

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% for i = 1:nsamples
%     ydata(i,:) = 5 + 10*cos(2*pi*time + pi/6);
% end
ydata       = 5 + 10*cos(2*pi*time + pi/6);
size(ydata)

ans = 1x2

1 2000

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plot(time, ydata), grid on