FFT of sine wave not plotting

clc;
spectrum=[];
omega=2*pi*10;
t=0:0.001:10;
f=0:0.1:500;

for n=1:0.001:10
    y(n)=sin(omega*y(n));
    spectrum=abs(fft((y)));
    for i=1:10001
        if spectrum(i)<5001
            spectrum2(i)=spectrum(i);
        end
        if spectrum(i)>5001
            spectrum3(i)=spetrum(i);
        end 
    end 
end
plot(f,spectrum);
hold on;
xlabel('frequency');
hold on;
ylabel('power');
hold on;
xlim([0 1]);

So I have a loop that stores 10001 values into an array. I need to be able to plot the values that are greater than, or less that 5001. I developed this code but its not working. Help is greatly appreciated!

[KALYAN ACHARJYA]

There are issues in the code, likewise

for n=1:0.001:10;
y(n)=

For the above n=1, first iteration will evaluate y(1)..OK

2nd interation n=0.001, which will evaluate y(0.001)..Not OK

Matlab only allows pisitive integer indexing, Hence , y(1), y(2), y(3)...so on...OK. But y(0),y(-2),y(0.04) are not allowed in Matlab Platform.

Plese do the modification, its easy to implement the code of FFT of sine wave

Answer 1

[Constantino Carlos Reyes-Aldasoro]

In addition to the previous comment 2 issues:

1) FFT will give a complex answer so you will need to plot the absolute values like

plot(abs(spectrum))

This is better than using the abs previously as you may need to use the phase, or imaginary parts for other calculations

2) you are looping as it is normally done in C or other programming languages. In Matlab you can do this as matrix operations, no need to loop

omega=2*pi*10;
t=0:0.001:10;

y=sin(omega*t);
spectrum=fft(y);

spectrum2=spectrum(1:5000);
spectrum3=spectrum(5001:end);
plot(abs(fftshift(spectrum)))

also notice that you had a typo

spectrum3(i)=spetrum(i);