Error using indexing Invalid indexing or function definition. Indexing must follow MATLAB indexing.

I encounter "Error using indexing

Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic

variables, and function body must be sym expression.

Error in modified_signal (line 54)

B(w) = fourier(b(t), w);" with this script when using symbolic function, the signal A(w), a(t), and b(t) do not have any issue, but B(w) has caused the error. Any solution to overcome this issue? Thank you.

%create symbolic functions x, a, b, c, d, e, f_c with independent variable t
syms x(t) a(t) h(t) b(t) c(t) d(t) e f_c(t) f_c1(t) f_c2(t) t tau
%create symbolic functions A, B, C, D, and E with independent variable w
syms A(w) B(w) C(w) D(w) E(w) w
x(t) = cos(100*pi*t);
a(t) = x(0.4*t);
h(t) = dirac(t-0.02);
b(t) = int(a(tau)*h(t-tau), 'tau', -inf, inf);
f_c(t) = 10*cos(2500*pi*t);
f_c1(t) = f_c(t);
f_c2(t) = f_c(t);
c(t) = b(t)*f_c1(t);
d(t) = c(t)*f_c2(t);
figure
subplot (2,1,1)
fplot(a(t))
xlim([-0.05 0.05]),ylim([-1.5 1.5])
title ('Time domain of signal a(t)')
xlabel('Time, t')
ylabel('Amplitude, a(t)')
grid on
A(w) = fourier(a(t), w);
w = -60*pi:0.1*pi:60*pi;
subsA = A(w);
% Replace Inf value with suitable value
idx = subsA == Inf;
subsA(idx) = pi; % choose suitable value from the expression of fourier transform.
subplot (2,1,2)
plot(w,real(subsA));
ylim([0 3.5])
title ('Time domain of signal A(\omega)')
ylabel("\Re(A(\omega))");
xlabel("\omega");
xticks(-40*pi:20*pi:40*pi);
xticklabels({'-40\pi', '-20\pi', '0', '20\pi', '40\pi'})

figure
subplot(2,1,1)
fplot(b(t))
xlim([-0.05 0.05]),ylim([-1.5 1.5])
title ('Time domain of signal b(t)')
xlabel('Time, t')
ylabel('Amplitude, b(t)')
grid on

B(w) = fourier(b(t), w);

Error using indexing
Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression.

w = -60*pi:0.1*pi:60*pi;
subsB = B(w);
% Replace Inf value with suitable value
idx = abs(subsB) == Inf;
subsB(idx) = pi; % choose suitable value from the expression of fourier transform.
subplot (2,1,2)
plot(w,real(subsB));
ylim([0 3.5])
title ('Time domain of signal B(\omega)')
ylabel("\Re(B(\omega))");
xlabel("\omega");
xticks(-40*pi:20*pi:40*pi);
xticklabels({'-40\pi', '-20\pi', '0', '20\pi', '40\pi'})
figure
subplot(2,1,1)
fplot(c(t))
xlim([-0.05 0.05]),ylim([-12 12])
title ('Time domain of signal c(t)')
xlabel('Time, t')
ylabel('Amplitude, c(t)')
grid on
figure 
subplot(2,1,1)
fplot(d(t))
xlim([-0.1 0.1]),ylim([-110 110])
title ('Time domain of signal d(t)')
xlabel('Time, t')
ylabel('Amplitude, d(t)')
grid on

Answer 1

[VBBV]

%create symbolic functions x, a, b, c, d, e, f_c with independent variable t
syms x(t) a(t) h(t) b(t) c(t) d(t) e f_c(t) f_c1(t) f_c2(t) t tau
%create symbolic functions A, B, C, D, and E with independent variable w
syms A(w) B(w) C(w) D(w) E(w) w
x(t) = cos(100*pi*t);
a(t) = x(0.4*t);
h(t) = dirac(t-0.02);
b(t) = int(a(tau)*h(t-tau), 'tau', -inf, inf)

b(t) = 

f_c(t) = 10*cos(2500*pi*t);
f_c1(t) = f_c(t);
f_c2(t) = f_c(t);
c(t) = b(t)*f_c1(t);
d(t) = c(t)*f_c2(t);
figure
subplot (2,1,1)
fplot(a(t))
xlim([-0.05 0.05]),ylim([-1.5 1.5])
title ('Time domain of signal a(t)')
xlabel('Time, t')
ylabel('Amplitude, a(t)')
grid on
A(w) = fourier(a(t), w);
w = -60*pi:0.1*pi:60*pi;
subsA = A(w);
% Replace Inf value with suitable value
idx = subsA == Inf;
subsA(idx) = pi; % choose suitable value from the expression of fourier transform.
subplot (2,1,2)
plot(w,real(subsA));
ylim([0 3.5])
title ('Time domain of signal A(\omega)')
ylabel("\Re(A(\omega))");
xlabel("\omega");
xticks(-40*pi:20*pi:40*pi);
xticklabels({'-40\pi', '-20\pi', '0', '20\pi', '40\pi'})

figure
subplot(2,1,1)
fplot(b(t))
xlim([-0.05 0.05]),ylim([-1.5 1.5])
title ('Time domain of signal b(t)')
xlabel('Time, t')
ylabel('Amplitude, b(t)')
grid on
syms w
B(w) = fourier(b(t), w);
w = -60*pi:0.1*pi:60*pi;
subsB = B(w);
% Replace Inf value with suitable value
idx = abs(subsB) == Inf;
subsB(idx) = pi; % choose suitable value from the expression of fourier transform.
subplot (2,1,2)
plot(w,real(subsB));
ylim([0 3.5])
title ('Time domain of signal B(\omega)')
ylabel("\Re(B(\omega))");
xlabel("\omega");
xticks(-40*pi:20*pi:40*pi);
xticklabels({'-40\pi', '-20\pi', '0', '20\pi', '40\pi'})

figure
subplot(2,1,1)
fplot(c(t))
xlim([-0.05 0.05]),ylim([-12 12])
title ('Time domain of signal c(t)')
xlabel('Time, t')
ylabel('Amplitude, c(t)')
grid on

figure 
subplot(2,1,1)
fplot(d(t))
xlim([-0.1 0.1]),ylim([-110 110])
title ('Time domain of signal d(t)')
xlabel('Time, t')
ylabel('Amplitude, d(t)')
grid on