MATLAB: Finding peaks in data based on certain threshold

finding peaks above certain values

Hi I have an array [V Data] (Attached data file).The plot is shown below.

I want to detect the # of peaks (3 in this case) which are above a certain threshold (value is = 0.1) I also want to find the points where it crosses the threshold and extract respective values from V

Thanks SATEJ

Best Answer

Once I had to write a function for this type of problem in on of my projects. Seeing your question here, I have uploaded that file in file exchange:

http://www.mathworks.com/matlabcentral/fileexchange/48818-peak-detection-of-a-function

Just use your +/-TestV as x, Data as y in the function, and threshold as 0.1. Ignore the outputs for minima.

By the way, if you have a closer look at your figure, there are two small peaks in 'left side', one big peak in 'middle', and one smaller peak at the 'right'. So, there will be 4 peaks in total instead of 3. Plot this data in Matlab, and enlarge the figure to verify this observation.

I guess, if you use the linked function findpeaks, the result will be 4 as well. You could also see the x coordinate at which peaks occur, and also the peak values at those points.

Related Solutions

MATLAB: Return curve peak coordinates – not just the peak

I would do something like this:

x = [1:17]*10;                                                  % Create Data

y = [0 1 0 2 0 9 0 3 0 1 0 2 0 9 0 3 0]*0.25;                   % Create Data
[pks1,locs1] = findpeaks(y, x, 'MinPeakHeight',2);
[pks2,locs2] = findpeaks(-y, x);
pk1_start = locs2(find(locs2 < locs1(1), 1, 'last'));           % Start Of First Peak
pk1_end = locs2(find(locs2 > locs1(1), 1, 'first'));            % End Of First Peak

... then do the same for the second peak, ‘locs1(2)’. With the start- and end-points, you can define the entire peak.

This makes some assumptions about your data, since I do not have them to work with. You will probably have to experiment with this idea for it to work with your data.

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: Return curve peak coordinates – not just the peak

MATLAB: Flipping y-axis of findpeaks-plot

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