how to find peaks for 100%,75%,50%,25% of the max peak

Hi good day.. i am having trouble in identify the 100%,75%,50%,25% of the peaks of my data(only need to identify 4 peaks).Hope anyone can help me to solve the problem.Thank you in advance

• VINCENT NORMALISED MC.txt

f = 'file:///C:/Users/user/Documents/VINCENT%20NORMALISED%20MC.txt';

M = readmatrix(f);

x = M(:,1);

y = M(:,2);

tiledlayout('flow');

nexttile;

plot(x,y);

nexttile;

y2 = smoothdata(y);

plot(x,y2);

findpeaks(y2)

[KSSV]

Attach your data.

[Keshasni Earichappan]

attached data

Answer 1

[Kevin Holly]

I'm not entirely sure what peaks you are trying to identify. Below are techniques you can use.

You can add labels to your peaks to help you identify them. You can also set a minimum peak prominence.

findpeaks(y2,'MinPeakProminence',4) % adds peak labels to graph
[pks,locs,w,p] = findpeaks(y2,'MinPeakProminence',4) %obtains informations about peaks
text(locs+.02,pks,num2str((1:numel(pks))')) % place text next to labels

From the labels, it is clear the top four peaks in value with the settings above are 4, 6,17, and 21.

top4peaks = [4 6 17 21];
nexttile;
plot(x,y2);
findpeaks(y2,'MinPeakProminence',4)
text(locs(top4peaks)+.02,pks(top4peaks),num2str(top4peaks'))

[pks(top4peaks),locs(top4peaks),w(top4peaks),p(top4peaks)]

nexttile;
plot(x,y2);
findpeaks(y2,'MinPeakProminence',40)

Edit: I just saw in title that you want 100%,75%,50%,25% of the max peak

Find max peak with this command

[value index] = max(pks)

75%, 50%, and 25%

pks(abs(pks-.75*value)==min(abs(pks-.75*value)))
pks(abs(pks-.50*value)==min(abs(pks-.50*value)))
pks(abs(pks-.25*value)==min(abs(pks-.25*value)))

[Keshasni Earichappan]

hi @Kevin Holly..thanks for the answer...I'm confused with your code as i mentioned below...what is the value index :)

[value index] = max(pks);

pks(abs(pks-.75*value)==min(abs(pks-.75*value)))

pks(abs(pks-.50*value)==min(abs(pks-.50*value)))

pks(abs(pks-.25*value)==min(abs(pks-.25*value)))

[Kevin Holly]

[value, index] = max(pks);

"value" returns the maximum value the the array, "pks".

"index" returns the index into the operating dimension that corresponds to the maximum value of "pks" for any of the previous syntaxes.

Answer 2

[KSSV]

T = readtable('VINCENT NORMALISED MC.txt') ; 
x= T.(1) ; y = T.(2) ; 
% find max 
[val,idx] = max(y) ; 
% find 75, 50 and 25 of max 
vals = val*[75 50 25]/100 ;
idx = knnsearch(y,vals') ;

plot(x,y)
hold on
plot(x(idx),y(idx),'*r')