why am I getting "Array indices must be positive integers or logical values"

clear 
syms t; 
Fs=5; 
T=1/Fs; 
L=1500; 
t=(0:L-1)*T; 
Yo=4+4.005*(sin(t)+sin(3*t)/3+sin(5*t)/5+sin(7*t)/7); 
y = fft(Yo); 
f=2*pi*Fs(0:(L/2))/L; 

Array indices must be positive integers or logical values.

p2 = abs(y/L); 
p1=p2(1:L/2+1); 
p1(2:end-1) = 2*p1(2:end-1); 
%f=2*pi*Fs(0:(L/2))/L; 
plot(f,p1) 
title ('Amplitude Spectrum') 
xlabel('time') 
ylabel('y(t)')

[Cris LaPierre]

syms t is doing nothing here. You can remove it.

Answer 1

[Voss]

You were indexing Fs with a vector that had a 0 in it. Looks like you meant to be multiplying Fs by that vector instead:

clear 
syms t; 
Fs=5; 
T=1/Fs; 
L=1500; 
t=(0:L-1)*T; 
Yo=4+4.005*(sin(t)+sin(3*t)/3+sin(5*t)/5+sin(7*t)/7); 
y = fft(Yo); 
% f=2*pi*Fs(0:(L/2))/L; % <- indexing
f=2*pi*Fs*(0:(L/2))/L; % <- multiplying
p2 = abs(y/L); 
p1=p2(1:L/2+1); 
p1(2:end-1) = 2*p1(2:end-1); 
%f=2*pi*Fs(0:(L/2))/L; 
plot(f,p1) 
title ('Amplitude Spectrum') 
xlabel('time') 
ylabel('y(t)')

Answer 2

[Jan]

The variable Fs has the value 5. Then the expression:

Fs(0:(L/2))

is treated as indices. 0 is not a valid index. In addition Fs is a scalar and indexing cannot work apart from the index 1.

Maybe you mean:

Fs * (0:(L/2))

Answer 3

[Image Analyst]

Full explanation in the FAQ:

https://matlab.fandom.com/wiki/FAQ#.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22