how to plot this function

[darova]

Do you have any attempts?

[HADIMARGO]

Yes sir. But it didnot give me the right shape:

[HADIMARGO]

[Walter Roberson]

(n<-2 & n>2)

is never true. However, since you are multiplying that by 0, if it somehow did match it would contribute 0 anyhow. You can just leave out that term.

Your x axis is wrong. You are effectively using your n as your frequency, including negative n. If you are going to plot negative frequencies then you need to fftshift() . And use more points.

Read the first example of fft() to see how to properly plot.

Answer 1

[Sulaymon Eshkabilov]

n = -5:1:5; 
x=1*(n>=-2 & n<=2)+0*(n<-2 & n>2);
L = length(n); Fs = 1;
Nblock = 128; % Block size
Y = fft(x, Nblock)/L;
f = Fs/2*linspace(0,5, Nblock/2+1);
plot(f, 2*abs(Y(1:Nblock/2+1)))
xlabel('frequency, [Hz]'), ylabel('Amplitude') 
title('Single-sided Spectrum'), shg

[madhan ravi]

x=1*(n>=-2 & n<=2)+0*(n<-2 & n>2); % what is the necessity to multiply it by zero ?? 
% Hint: Not necessary

[HADIMARGO]

so many tnx for ur answering. but why the shapes didnot match together?

[HADIMARGO]

hi.

i could find this code that the result and shape is near to my shape.

clc
clear


t=linspace(-5,5,100);

y=heaviside(t+0.5)-heaviside(t-0.5);

z=fft(y);

z=abs(z);

stem(z)

Answer 2

[Sulaymon Eshkabilov]

Hi,

Here is the full spectrum calculation:

n = -5:1:5; 
x=1*(n>=-2 & n<=2);
L = length(n); Fs = 1;
Nblock = 128; % Block size
Y = fft(x, Nblock)/L;
f = Fs/2*linspace(0,5, Nblock);
plot(f, 2*abs(Y(1:Nblock)))
xlabel('frequency, [Hz]'), ylabel('Amplitude') 
title('Single-sided Spectrum'), shg

Good luck.

[HADIMARGO]

tnx. this is so near also to final shape but my result is:

[Walter Roberson]

fftshift()

[HADIMARGO]

can u explain more mr Walter Roberson.

[Walter Roberson]

t = linspace(0,10);
ft = fft(t);
subplot(1,2,1); plot(abs(ft));   %what you are doing now
subplot(1,2,2); plot(abs(fftshift(ft)));   %what you need to do in order to get the 0 in the center