MATLAB: Finding prominent maxima and minima of a column vector

prominent max min

Hello,

Suppose I Have a column vector wcich has multiple maxima and minima, I just want to find the index of N= 4 number of them ( prominent maxia and minima).

And if I use something like 'findpeak' then it gives a lots of local max and min as for a noisy signal. I want to get the prominant max & min indices of the 2nd colm of the attachment please.

Thank you

Best Answer

Although findpeaks needs some help here, it can find all four:

[D,S] = xlsread('ab1.xlsx');
[pks,plocs] = findpeaks([D(:,2); min(D(:,2))], 'MinPeakProminence',1);   % Append ‘0’ To Far End To Identify Last Peak
[vls,vlocs] = findpeaks(-D(:,2), 'MinPeakProminence',1)
figure
plot(D(:,1), D(:,2))
hold on
plot(D(plocs,1), pks, '^r')
plot(D(vlocs,1), vls, 'vr')
hold off
grid
legend('Data','Peaks','Valleys')

The associated times are: D(plocs,1).

Similarly for the valleys:

Related Solutions

MATLAB: How to save each loop variable in the same vector

%data set = x 
n = 24;
M = numel(x)-n+1;
all_vi = zeros(1,M);
all_fi = zeros(1,M);
for i = 1:M
    xi = x(i:i+23);
    envelope(xi,1,'peak');
    [peakHeights,valleyHeights] = envelope(xi,1,'peak'); 
    vi = sum(peakHeights-valleyHeights);
    [peakHeights, indexesOfPeaks] = findpeaks (xi); 
    [valleyHeights, indexesOfValleys] = findpeaks (xi); 
    fi = numel(indexesOfPeaks) + numel(indexesOfValleys);
    all_vi(i) = vi;
    all_fi(i) = fi;
end

MATLAB: Flipping y-axis of findpeaks-plot

You may be making this too difficult.

Example —

a = linspace(0, 4*pi);
y = sin(a);
[pks,pkloc] = findpeaks( y,a);                          % Maxima
[vls,vlloc] = findpeaks(-y,a);                          % Minima

figure(1)
plot(a, y, '-b')
hold on
plot(pkloc, pks, '^r', 'MarkerFaceColor','r')
plot(vlloc, -vls, 'vg', 'MarkerFaceColor','g')
hold off
grid
axis([xlim    -1.1  1.1])
legend('Data', 'Peaks', 'Valleys')

Note that to plot the valleys (‘vls’) or minima correctly, simply negate them in the plot call. So to find them, use:

[vls,vlloc] = findpeaks(-y,a);                          % Minima

and to plot them or use them in other calculations correctly, negate them again to restore their correct values:

plot(vlloc, -vls, 'vg', 'MarkerFaceColor','g')

Best Answer

Related Solutions

MATLAB: How to save each loop variable in the same vector

MATLAB: Flipping y-axis of findpeaks-plot

Related Question