Here is the corrected code. Time domain vs. Frequency domain analysis of the signal t vs. xx:
load firlab2
%%
input = xx;
dt = t(2)-t(1); % Sampling time, [s]
fs = 1/dt; % Sampling frequency, [Hz]
N = length(t); % Signal length
F = abs(fft(input))/N; % Signal spectrum
F1 = F(1:N/2+1);
F1(2:end-1) = 2*F1(2:end-1);
f = fs*(0:(N/2))/N; % Frequency data
subplot(211)
plot(t, input, 'b-') % Input signal in Time domain
xlabel('\it Time, [s]')
ylabel('\it Amplitude')
title 'Signal in time domain'
grid on
subplot(212)
plot(f,F1) % Input signal spectrum in frequency domain
title('Single-Sided Amplitude Spectrum of Signal ')
xlabel('\it Frequency, [Hz]')
ylabel('\it Amplitude of Spectrum')
grid on
