How to fix: "Index exceeds matrix dimensions"?

I want to use fft on first cycle of sine wave to get all samples from it.

fs=1000;
t = 0:1/fs:0.2-1/fs;
x = 5*sin(2*pi*50*t);
plot(t,x)

To do it I used loop:

n = 20;
for i=n:length(x)
y = fft(x(i:i+n-1));
end

where n is number of samples/cycle (fs=1000, freq=50 Hz).

But MATLAB shows me an error "Index exceeds matrix dimensions" in line with y = fft(...).

How to fix it?

Answer 1

[Cris LaPierre]

It means you are indexing into x with a number that exceeds the size of x.

Checking the size of x, it is 1x200. Check the value of "i" when your code stops running. I get 182. Your index is

x(i:i+n-1)

or, when it errors out,

x(182:182+20-1)
x(185:201)

x(201) does not exist. Hence the error message.

the fix is to adjust your indexing so you doen't exceed 200.