Index exceeds the number of array elements (0)

When I run this code, there is a problem like this:

Index exceeds the number of array elements (0).

Error in Untitled9 (line 39)

plot (t,abs(Xn(1:k)));

And this is a code:

clc;
close all;
Fs=500;
Ts=1/Fs;
Tsin=3;
t=0:Ts:1-Ts;
x1n=cos(50*pi*t);
t=1:Ts:2-Ts;
x2n=cos(50*pi*t)+cos(100*pi*t);
t=2:Ts:3-Ts;
x3n=cos(50*pi*t)+cos(100*pi*t)+cos(150*pi*t);
t=3:Ts:Tsin;
xn=[x1n x2n x3n zeros(size(t))];
M=128;
L=30;
Nx=length (xn);
k=(Nx-L)/(M-L);
k=floor(k);
R=M-L;
g=gausswin(M);
Xn=[];
for n=1:k
    X=xn(((n-1)*R+1):(n-1)*R+M);
    Xm=fft(X,M);
    figure(1);
    plot3(repmat(n,1,M),1:M,abs(fft(X,M)));
    hold on
end

t=0:Ts:Tsin;
figure(2)
subplot(1,2,1);
plot(t,xn);
xlabel('t(s)');
ylabel('Amplitude');
title ('Input sequence');
subplot (1,2,2);

plot (t,abs(Xn(1:k)));

Index exceeds the number of array elements. Index must not exceed 0.

xlabel('t(s)');
ylabel('Amplitude');
title('STFT');

How to solve this problem? Please help me

Answer 1

[Cris LaPierre]

The problems is you are trying to index an empty array. You define Xn=[]; and never assign it a value, but then try to index it like it has a value.

Is Xm a typo? Did you mean to use Xn? If so, note that I had to adjust the number of t values to make the number of Xn values in the plot command: both have to have 1:k values.

clc;
close all;
Fs=500;
Ts=1/Fs;
Tsin=3;
t=0:Ts:1-Ts;
x1n=cos(50*pi*t);
t=1:Ts:2-Ts;
x2n=cos(50*pi*t)+cos(100*pi*t);
t=2:Ts:3-Ts;
x3n=cos(50*pi*t)+cos(100*pi*t)+cos(150*pi*t);
t=3:Ts:Tsin;
xn=[x1n x2n x3n zeros(size(t))];
M=128;
L=30;
Nx=length (xn);
k=(Nx-L)/(M-L);
k=floor(k);
R=M-L;
g=gausswin(M);
Xn=[];
for n=1:k
    X=xn(((n-1)*R+1):(n-1)*R+M);
    Xn=fft(X,M);
    figure(1);
    plot3(repmat(n,1,M),1:M,abs(fft(X,M)));
    hold on
end

t=0:Ts:Tsin;
figure(2)
subplot(1,2,1);
plot(t,xn);
xlabel('t(s)');
ylabel('Amplitude');
title ('Input sequence');
subplot (1,2,2);
plot (t(1:k),abs(Xn(1:k)));
xlabel('t(s)');
ylabel('Amplitude');
title('STFT');

[Trinh Bac]

thank you

Answer 2

[the cyclist]

You have confusingly defined both Xn and xn. You are trying to access the variable Xn, which is an empty array.

I'm guessing you intended to access xn instead, but I haven't tried to figure out what you actually wanted to do.