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How to find the maximum of peaks ?

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Ramesh Bala
Ramesh Bala on 18 Aug 2021
Commented: Ramesh Bala on 19 Aug 2021
I want to find the first maximum 4 peaks in loop.My code finds all the peaks,how can I find only 4 and plot them ?
A= load ('ZT2.mat');
figure
for i= 1:1:300
s3= abs(fft( A.A1(:,i)));
subplot (3,2,1)
plot (s3((1:end/2)));
subplot (3,2,2)
[pkSA{i},locSA{i}]=findpeaks(s3);
plot ( (locSA{i}),(pkSA{i}));
title('Peaks ZT1');
drawnow
pause(0.1)
end

Accepted Answer

Yazan
Yazan on 18 Aug 2021
Below, I am proposing an implementation of what I understood to be your task. You have to experiment with the findpeaks multiple options to find a setting good for your data.
clc, clear
load ('ZT2.mat');
figure
fftData = abs(fft(A1, [], 2));
N = size(fftData, 2);
fftData = [fftData(:, 1:N/2), fftData(:, 1)];
freq = linspace(0, 0.5, N/2+1);
locSA = cell(1, size(A1, 1));
pkSA = cell(1, size(A1, 1));
Np = 4;
sortP = 'descend';
minPeakDis = 1;
for i=1:size(fftData,1)
[pkSA{i}, locSA{i}] = findpeaks(fftData(i,:), 'NPeaks', 4, 'SortStr', sortP, ...
'MinPeakDistance', minPeakDis);
subplot (1, 2, 1)
plot(freq, fftData(i,:)); xlabel('Normalized frequency')
ylabel('Amplitude'), title('Positive spectrum')
hold on, plot(freq(locSA{i}), pkSA{i}, 's', 'MarkerSize', 5, 'MarkerEdgeColor', 'g',...
'MarkerFaceColor', 'g'); grid minor, hold off
subplot (1, 2, 2)
stem(freq(locSA{i}), pkSA{i}, 'Marker', 's', 'MarkerSize', 7, 'MarkerEdgeColor', 'g',...
'MarkerFaceColor', 'g'); xlabel('Normalized frequency')
ylabel('Amplitude'), title('Spectral peaks locations'), grid minor
drawnow
pause(1)
end
  1 Comment
Ramesh Bala
Ramesh Bala on 19 Aug 2021
This is perfect .Thanks Yazan
this the key that I was expecting especially 'SortStr', sortP, ...
'MinPeakDistance', minPeakDis

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