I got error with "error using plot, vectors must be the same length"

[dpb]

Did you even look to see what you have done???

T=10;
Ts=0.01;
t=-T:Ts:T;
x=square(2*pi*t);
X=fft(x);
f=(-1/(2*Ts):1/Ts:1/(2*Ts))

f = 1×2

-50 50

m=abs(fftshift(X));
numel(f), numel(m)

ans = 2

ans = 2001

Answer 1

[Paul]

Hi Tran,

Next time, please copy/paste your code into the Question, which makes it much easier for people to help.

Original code

T = 10;
Ts = 0.01;
t = -T:Ts:T;
x1 = square(2*pi*t);
X1 = fft(x1);

frequencies = fftshift(-1/(2*Ts):1/Ts:1/(2*Ts));
magnitude_spectrum = abs(fftshift(X1));

Number of elements in the vectors

numel(frequencies)

ans = 2

numel(magnitude_spectrum)

ans = 2001

So the error arises becasue 2001 elements can't be plotted against 2 elements.

The correct expression for frequencies in this case would be, assuming units of rad/sec which looks like what might be wanted

frequencies = (-1000:1000)/2001/Ts;

Also, because x1 is defined from -T to T, it's likely that ifftshift should be applied to x1 before taking its fft.