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datab = hor950_zoneb;
PS=fft(datab);
PS(1)=[];
n=length(PS);
power = abs(PS(1:floor(n/2))).^2;
nyquist = 1/2;
freq = (1:n/2)/(n/2)*nyquist;
period=1./freq;
plot(period,power);
ylabel('Densité Spectral');
xlabel('Period (jour/Cycle)');
grid on;
title('FFT Zone b')
hold on;
index=find(power==max(power));
mainPeriodStr=num2str(period(index));
plot(period(index),power(index),'r.', 'MarkerSize',25);
text(period(index)+2,power(index),['Period = ',mainPeriodStr]);
hold off;
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