What is the problem in this code?

f0=100;
f=(0:f0/40:f0*2);
Ts=1/fs;
n=0:8;
xs = 5*cos(2*pi*f0*n*Ts);
i=fft(xs);
plot(f,abs(i(1:81)))

[Hassan Ali Shah]

it gives the error Index exceeds matrix dimensions.

Error in Untitled (line 7) plot(n,abs(i(1:81)));

Answer 1

[Shoaibur Rahman]

Your n has a length of 9, as n=0:8, so i will have length of 9 as well,and hence, you cannot write i(1:81). There are many ways to solve this. Here is one: replace n = 0:8 by n = linspace(0,8,length(f)). This will make both f and i of same length.

Also, although plot(f,abs(i(1:81))) works fine, but you can simply use plot(f,abs(i))

Another way may be: keep everything same, but write i = fft(xs,length(f)) . This will perform 81 point fft on xs. Again, you can use plot(f,abs(i))

[Hassan Ali Shah]

thanks dear. it worked.though both the ways are doing good,but your "another way" suits me more. thanks alot