How can I set a descend order finding peaks to my graph ?

Question

Ramesh Bala 2019-9-26

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/482273-how-can-i-set-a-descend-order-finding-peaks-to-my-graph

评论： Ramesh Bala 2019-10-1

I have a graph that takes the values from first maximum peak point and plots it.Now,how shall i introduce a threshold or descend order from that point,so that it find the next highest peak ?

load('signal')
load('t')
S(:,1)=[ 5 15 35 45 5 15 35 45];
S(:,2)=[ 5 15 15 5 45 35 35 45];
 for k=1:1:length(S) 
[a(k),b2(k)]=max(abs(hilbert(signal(k,:)))); % first peak amp & index
    
 [PkAmp, PkTime] = findpeaks(abs(hilbert(signal(k,:))),t); 
  
  peaks(1,1)=a(k);
  peaks(2,1)=t(b2(k));
  
 j=2;
 for i=1:length(PkTime)   
 if PkTime(i)>t(b2(k))
     peaks(1,j)=PkAmp(i);
     peaks(2,j)=PkTime(i);
     j=j+1;
 end
 end
figure;  
    plot(t,(signal(k,:)),t,abs(hilbert(signal(k,:))),peaks(2,1),peaks(1,1),'ro')
    hold on;grid on
    plot(PkTime, PkAmp, '^r', 'MarkerFaceColor','r')
    xlim([0 0.0006]);ylim([-inf inf])
    hold on,plot(peaks(2,3),peaks(1,3),'ko')
    
 end
 
 

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darova 2019-9-26

What if just use findpeaks() two times?

[y, ix] = findpeaks(origin_data);
[y1,ix1] = findpeaks(y);
i = ix(ix1);
plot(time,origin_data)
hold on
plot(time(i),origin_data(i),'^r')
hold off

Ramesh Bala 2019-9-27

Thanks Darova for the comment.

It doesn't work as it didn't made any envelope over it.

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Answer 1

Akira Agata 2019-9-26

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/482273-how-can-i-set-a-descend-order-finding-peaks-to-my-graph#answer_393684

How about combining envelope and findpeaks functions?

The following is an example.

% Load data
load('signal.mat');
load('t.mat');
% Calculate envelope and detect it's peaks
ul = envelope(signal(1,:));
[pks,locs] = findpeaks(ul,t,'MinPeakProminence',0.5e-3);
% Show the result
figure
plot(t,signal(1,:))
hold on
plot(t,ul)
scatter(locs,pks,'rv')
legend({'Original data','Envelope','Peaks'},'FontSize',12)

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Ramesh Bala 2019-9-27

编辑：Ramesh Bala 2019-9-27

Thanks Akira Agata for the answer.

Indeed it looks promising.But if you check the figure it didn't took the next sharp peak as 3rd put took in another period peak.

Also,this is one signal,but when I do it in a loop for all the 8 signals,it even takes the value before the highest envelope point.I tried to increase ,decrease the minpeak prominence value to 0.4e-3-0.7e-3 range still not satisfactory.I have to atleast check if this works for 6 peaks.The perfect one was figure6,figure 5,8 takes the peak values before the envelope max. Attaching figure1 and figure6,7,8 from the code.

Reattaching the code with the loop

 % Load data
load ( 'signal.mat' );
load ( 't.mat' );
% Calculate envelope and detect it's peaks
for k=1:1:length(signal)
ul = envelope (signal (k, :));
[pks, locs] = findpeaks (ul, t, 'MinPeakProminence' , 0.5e-3);
% Show the result
figure
plot (t, signal (k, :))
hold on
plot (t, ul)
scatter (locs, pks, 'rv' )
legend ({ 'Original data' , 'Envelope' , 'Peaks' }, 'FontSize' , 12)
end

With minpeakprominence value =0,5e-3

Peak 2 is correct ,but 3.4 seems not identifed and 5thor 4th valyeis identifed as 3rd.

Correctly identified peaks-fig 6 - all 6 peaks clearly shown

Fig 5: negative peak identified

Fig 8:negative peak identified

Ramesh Bala 2019-9-30

Thank you ! it works well for most signals !

I would like to know how to set that Minpeak prominence ,could you elaborate how to identify it and its significance.

Ramesh Bala 2019-10-1

I would like to know how can I further choose different peak values and store them in a separate variable.

Currently pks0(pt) and locs0(pt) is stored as a variable in a linear way according to signal numbers.

But,is there a way using brush option or something to select single peak from a figure and store it as (1,1) and then another peak from another plot and store as (1,2)