The fastest way to find local minimum

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Hg
Hg on 20 Oct 2015
Commented: Hg on 20 Oct 2015
What is the most efficient/fastest way to find the circled local minimum below, the lowest minima between two highest peaks? The graph was created by plot(x,y).
  5 Comments
Walter Roberson
Walter Roberson on 20 Oct 2015
Never name a variable "min"; that interferes with using the MATLAB min() function. For example,
[peaks, locs] = findpeaks(x, y,'MinPeakProminence',100);
[minval, minidx] = min( x(locs(1):locs(2)) );
%minidx is relative to the subset of values, so move it back to full range
minidx = minidx + locs(1) - 1;
Hg
Hg on 20 Oct 2015
Edited: Hg on 20 Oct 2015
Thanks for the advice. I think using 'MinPeakProminence' to get 2 highest peaks is not robust enough. It might get more than 2 peaks like below where the first and second peak have same value.

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Accepted Answer

Image Analyst
Image Analyst on 20 Oct 2015
Invert your signal
invertedSignal = max(signal(:)) - signal;
Now valleys will be peaks. Then call find peaks.

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