Hello Vicente,
You can try a couple of different approaches:
Option A: Use findpeaks function to get the values of the peaks and compute the differences to obtain the amplitude and the period.
x=Tm(4000:5000);
y=P01m(4000:5000);
[Mpy,Mpx]=findpeaks(y); % Find local maximums
[mpy,mpx]=findpeaks(-y);% Find local minimums
T=mean(diff(x(Mpx))); % Period
A=mean(y(Mpx)-y(mpx(1:end-1)))*0.5; %Amplitude
toppeak=mean(Mpy); %Max peak value
Option B: Fit your data into a sinusoidal and use the parameters to obtain the desired values
fitfun = fittype( @(a,b,x) a*sin(b*x+c)); % Define the sinusoidal
[fitted_curve] = fit(x,y,fitfun,'StartPoint',[5.3,6.97,-7.6])
plot(x,y,'.') %Plot the model to ensure the fit works
hold on
plot(x,fitted_curve(x))
A=fitted_curve.a; % Amplitude of your wave
T=2*pi/fitted_curve.b; % Period = 2pi/f
