Extract peaks and troughs from a curve

How to extract only peaks and troughs from a curve

Answer 1

[Star Strider]

If you want to identify the individual peaks and troughs, use islocalmax and islocalmin, or findpeaks on the positive and negative versions of your signal respectively:

[pks, pklocs] = findpeaks(s);
[troughs,trlocs] = findpeaks(-s);

where ‘s’ is youir signal vector.

[Mustafa Sobhy]

So how can I rearrange peaks and troughs consecutively like (peak, trough, peak, trough, ...) ?

Thanks!!

[Star Strider]

As always, my pleasure!

Create a matrix of the peaks, troughs and locations, then use sortrows:

[pks, pklocs] = findpeaks(s);                               % Original Peaks
[troughs,trlocs] = findpeaks(-s);                           % Original Troughs

pktr = [pklocs(:), pks(:); trlocs(:) -troughs(:)];          % Location, Value Matrix
pktrs = sortrows(pktr);                                     % Location, Value Matrix Sorted By Location

Since with findpeaks the troughs are detected using the negative of the original vector, their amplitudes in the ‘pktr’ matrix are negated to correct for that, presenting the actual values.

The sortrows function sorts by default on the first column. If you use a different configuration for ‘pktr’ you need to specify the column for the locations so that sortrows know which one to sort on.