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How can I find the local maximum and local minimum in my dataset?

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Farnood83 on 24 Jul 2021
Commented: Image Analyst on 25 Jul 2021
I have a dataset of Lateral Force vs Displacement from my experiments. I want to find the local maximums and local minimums in each set of data. Then I need to find the distance between the neighboring local minimum and local maximum. I attached some figures into my question and showed the local maximums and local minimums with circles. The local minimums have a black circle, and local minimums have a red circle.
Is it possible to use findpeaks or islocalmax? I think it might not be possible to use them because my data is not smooth.
Many thanks in advance

Accepted Answer

Image Analyst
Image Analyst on 24 Jul 2021
Depends on exactly what you mean by local min or max, and I don't see any black or red circles in the picture you posted. You could try movmin()/imerode() or movmax()/imdilate() to get the min or min in a moving window. The local min in the window may not necessarily be a valley and the local max may not necessarily be a peak. To get peaks and valleys you'd need islocalmin/islocalmax (very simple determination) or findpeaks for a more comprehensive classification of what you call a peak or value. To get valleys you need to invert your signal
[peakValues, indexesOfPeaks] = findpeaks(signal);
[valleyValues, indexesOfValleys] = findpeaks(-signal);
valleyValues = -valleyValues; % Invert back to get the original, non-negated values.
There are a bunch of complicated options in findpeaks() to fine tune what you consder a peak or valley.
Image Analyst
Image Analyst on 25 Jul 2021
Well whatever you want to find, those are the functions that will do it.

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