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

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

Cheers,

Answer 1

[Image Analyst]

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.

[Farnood83]

Many thanks for your reply. I attached the correct version of the picture.

Best,

Farnood

[Image Analyst]

It looks like you don't want the local min or max, or even ALL peaks, but just some peaks and valleys. So you want findpeaks(). Try the code I suggested but check out the documentation because there are a lot of tricky options to let you determine just how major or a peak you want, and then you can ignore some of the minor peaks.

[Farnood83]

Some of those are not actually the local maximum or local minimum. Those very small sharp parts of the data are not the main local maximums or local minimums. I just showed some of the major ones to explain what I mean. I will try your suggestion.

Thank you so much

Farnood

[Image Analyst]

Well whatever you want to find, those are the functions that will do it.