% This code is for Home exercise 3 of Advances in New Energy Technologies course (Spring 2022).
% All you need to do is to add correct file, i.e. name on line 6 (and change the label of y-axis on line 18).
% Do not change anything else from the code unless you know what you are doing.
% The data file has to be in the same folder where the code file is.

data = load('data1.txt');    % Loads the data file. 

N = length(data);                               % Number of data points
f = zeros(length(data), 1);                     % Initializing a vector for frequencies
CL = zeros(length(data), 1);                    % Initializing a vector for cycle lengths
t = 1;                                          % Time step between measurement points (1h)
h = 1:length(data);                             % Time moments of the measurement points

figure(1)                                       % These lines plot the data as a function of time
plot(h, data)
grid on;
xlabel('Time (h)')                              % Label of x-axis is the same for all datasets
ylabel('Solar radiation (W/m^2)')               % Label of y-axis can be changed here

ft = fft(data);                                 % This function performs a Fourier transform to the data
A = abs(ft);                                    % Calculates the amplitudes

for k = 1:N                                     % This loop calculates respective cycle length for each Ak
    f(k) = (k - 1) / (N * t);
    CL(k) = 1 / f(k); 
end

figure(2)                                       % These lines plot the amplitude of the Fourier transform 
plot(CL, A, '.-')                               % as a function of respective cycle length.
xlabel('Cycle length (h)')
ylabel('Amplitude')
grid on;