MATLAB: To find the first 3 local maximas of a plot/ dataset without the islocalmax and findpeaks

findpeaksislocalmaxlocalmaxlocalmaximamax

Hi, everyone

Is it possible to find the first 3 local maximas of a plot/ dataset without the islocalmax and findpeaks syntax?

Thanks in advance, Grace

Best Answer

Yes.

Is this for homework or an exam?

Related Solutions

MATLAB: Amplitude of non-periodic signal

Another possibility is in the code I used in this Answer. The peak times (the periods are the differences between them) will be in t(zx_idx) and the amplitudes will be in C(zx_idx) in that code.

MATLAB: To find the FWHM and area of pulses in a signal waveform

Try this:

M = readmatrix('z_data.xlsx');
t = M(:,1);
A = M(:,2);
As = smoothdata(A, 'movmean',15);                                       % Remove Noise
zci = @(v) find(v(:).*circshift(v(:), 1, 1) <= 0);                      % Returns Approximate Zero-Crossing Indices Of Argument Vector (>= R2016b)
dAdt = gradient(As)./gradient(t);                                       % Time Derivative
zx = zci(dAdt);                                                         % Zero-Crossing Indices
[pks,locs,fwhm,prmns] = findpeaks(A, 'MinPeakDistance',50);             % Return Full-Width-Half-Maximum Of Peaks
zx = [1; zx];                                                           % Modify ‘zx’ To Include First Index
Idx = zx(1:2:end);                                                      % Beginnings Of Each Peak
TotArea = cumtrapz(t,A);                                                % Integral
PkAreas = diff(TotArea(Idx));                                           % Peak Areas
PkLocs = locs(1:end-1);                                                 % Eliminate Last (Incomplete) Peak
PkTime = t(PkLocs);
Results = table(t(PkLocs), fwhm(1:end-1), PkAreas, 'VariableNames',{'PeakTime', 'FWHM', 'Area'});

Note: This code is reasonably robust, although fragile in that it may need to be modified slightly for different data sets. If there are incomplete peaks (that do not end in zero-crossings), or it begins with a complete peak (so that the initial index appears twice), those will need to be considered and corrected for in the calculation of the indices (‘zx’ and ‘locs’). It works as written for the data presented.

If you want to see graphically what the code does, plot this example:

figure                                                                  % Information Plot (Not Needed In Code)
plot(t, A)
hold on
plot(t, dAdt, '-r')
plot(t(zx), dAdt(zx), '+g')
plot(t(locs), pks, '^r')
hold off
grid
legend('Data', 'Detivative', 'Zero-Crossings', 'Peaks', 'Location','N')
xlim([ 0 750])
ylim([-5  30])

Best Answer

Related Solutions

MATLAB: Amplitude of non-periodic signal

MATLAB: To find the FWHM and area of pulses in a signal waveform

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