how is the frequency vector and index vector derived?

Hi All. I am trying to learn Fourier analysis and mathlab, I found the following piece of code on this forum but I can't seem to understand few lines in the code I was hoping you could help me understand.

first, how is the Fv Derived? can someone please help me understand what this piece code is doing

second, similary with index vector

and finally FTs_Plot ; why do we take the abs of FT(iv) dividing it with the maximum of itself?

i think I am able to understand what the rest of the code is doing except for those threee lines.

thanks in advance for your help.

D = load('time_domain.txt');
t = D(:,1);
s = D(:,2);
L = numel(t);                                                   % Vector Length
Ts = mean(diff(t));                                             % Sampling Interval
Fs = 1/Ts;                                                      % Sampling Frequency
Fn = Fs/2;                                                      % Nyquist Frequency
FTs = fft(s)/L;                                                 % Fourier Transform
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                             % Frequency Vector
Iv = 1:numel(Fv);                                               % Index Vector
FTs_plot = abs(FTs(Iv))/max(abs(FTs(Iv)));                      % Normalised Fourier Transform
figure
plot(Fv, FTs_plot)
grid
xlim([0 0.5])

[KSSV]

You try simly plotting plot(FTs).

The above will give you two symmetric frequency plots. We need to pick only half of the plot. The steps you have mentioned are to pick the half of the plot. And divison is to normalize the frequency plot.

[S Pro]

KSSV thanks for your response. Could you please break down and explain each line of code Fv, Iv and FTs_plot lines separerly please. I am confused specifically on those 3 lines.