How can i find the peak/maxima of a plot in just a selected region?

I have a plot of 2 vectors in a graph. I have to find the peak/maxima of just a small region. This region changes for different vectors. Can i choose that region somehow on the plot and find the correct peak?

Answer 1

[KSSV]

If you know the range of your values, use logical indexing and use max to get maximum in that region.

If you know the range of your maximum value, use findpeaks and pick the maximum/ peak value in your required range using logical indexing.

Answer 2

[Image Analyst]

If you have a vector and you know the starting and ending indexes of the region where you want to look, you can do

signal2 = signal; % Make copies of original
% Make outside the region minus infinity so we don't find anything there
signal2(1:startingIndex) = -inf;
signal2(endingIndex : end) = -inf;
% Find max value
maxValue = max(signal2);
% Find all the indexes where this value is located (there might be more than one)
indexesOfMax = signal2 == maxValue

Answer 3

[Star Strider]

I am not exactly certain what the problem is, however I am assuming that there are many peaks and the intent is simply to get the one in the region-of-interest.

I would do this in two steps —

First: Find the peak locations

Second: Isolate the peak in the region of interest

Example —

t = linspace(0, 10, 1E+3);                                          % Independent Variable
s = sin(2*pi*t/3) .* cos(2*pi*t/7);                                 % Signal
[pks,locs] = findpeaks(s)                                           % Detect Peaks (Use Appropriate Name-Value Pairs To Detect The Correct Peaks)

pks = 1×5

0.8178 0.5402 0.2351 0.9788 0.0290

locs = 1×5

63 250 485 679 888

idxv = randi(numel(t), 1, 2)                                        % Region-Of-Interest Index Begin & End Values

idxv = 1×2

782 905

idxrng = min(idxv) : max(idxv);                                     % Index Range VEctor
ChosenPeakIdx = locs( (locs>=min(idxrng)) & (locs <= max(idxrng)))  % Peak In Region-Of-Interest

ChosenPeakIdx = 888

figure
plot(t, s, 'DisplayName','Original Data')
hold on
plot(t(ChosenPeakIdx), s(ChosenPeakIdx), '^r', 'MarkerFaceColor','r', 'DisplayName','Selected Peak')
patch([t(idxrng) flip(t(idxrng))], [ones(size(idxrng))*min(ylim)  ones(size(idxrng))*max(ylim)], [1 1 1]*0.25, 'FaceAlpha',0.25, 'EdgeColor','none', 'DisplayName','Region-Of-Interest')
hold off
grid
legend('Location','best')

Experiment with the available data to get the desired results.

.