second largest peak value

2019 6 12
2 个回答
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更新时间：2019 8 6
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0 个投票

I'm getting the amp of second largest peak as correct but the time is wrong ?
How to obtain the second highest value X,Y from this and plot as already Y is correct ,X seems to be in wrong region?
s=load ('30827.mat');
signal(1,1:length(s.ans))=s.ans;
load t.mat;
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(1,:))),t);
[highestPeak, indexOfHighestPeak] = max(PkAmp);
[a(1),b2]=max(abs(hilbert(signal(1,:))));
[a2(1),b6]=max(PkAmp(PkAmp<max(PkAmp))); % to get second largest peak value
% error is the time value calcluate and plotted wrong??
Highesttime(1,:) = t(b2);
Highest2time(1,:) = t(b6);
figure;
plot(t,(signal(1,:)),t,abs(hilbert(signal(1,:))),t(b2),a(1),'ro')
hold on
plot(PkTime, PkAmp, '^r', 'MarkerFaceColor','r')
xlim([0 0.0006]);ylim([-inf inf])
grid on
hold on,plot(t(b6),a2(1),'ko')
hold off

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 采纳的回答

Alex Mcaulley
Alex Mcaulley 2019-6-12

1 个投票

To obtain the coordinates of the second peak you just need:
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(1,:))),t);
[~,idx] = sort(PkAmp,'descend');
PkAmp(idx(2)) %Amplitude of the second peak
PkTime(idx(2)) %Time of the second peak

13 个评论
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Ramesh Bala
Ramesh Bala 2019-6-12
Danke Schon Alex,
Lemme have a check
Ramesh Bala
Ramesh Bala 2019-6-12
Alright Alex ! I tried to use the method but it shows not compatible error ??
close all
s=load ('30827.mat');
signal(1,1:length(s.ans))=s.ans;
s= load ('30802.mat');
signal(2,1:length(s.ans))=s.ans;
load t.mat;
for k = 1:size(signal,1)
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(k,:))),t);
[a(k),b2]=max(abs(hilbert(signal(k,:))));
[a2(k),b6] = sort (PkAmp, 'descend' );
M(k) =PkAmp (b6(2)); % Amplitude of the second peak
Z(k) =PkTime (b6(2)); % Time of the second peak
figure;
plot(t,(signal(k,:)),t,abs(hilbert(signal(1,:))),t(b2),a(k),'ro')
hold on
plot(PkTime, PkAmp, '^r', 'MarkerFaceColor','r')
xlim([0 0.0006]);ylim([-inf inf])
grid on
hold on,plot(Z(k),M(k),'ko')
hold off
end
Ramesh Bala
Ramesh Bala 2019-6-12
编辑：Ramesh Bala 2019-6-12
Now it works well with some changes !!!But one question is how do i get the changing index values of b2 and b6 ,as it gives only the end values ( reason the X*Y matrix are not equal )
now it gives a single scalar value ,but I want all the index values b2 = [ xyx xyz] and b6 as such ??
close all
s = load ('30827.mat');
signal (1.1: length (s.ans)) = s.ans;
s = load ('30802.mat');
signal (2.1: length (s.ans)) = s.ans;
load t.mat;
for k = 1: size (signal, 1)
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(k,:))),t);
[a(k),b2]=max(abs(hilbert(signal(k,:))));
[a2, b6] = sort (PkAmp, 'descend' );
M(k)=PkAmp (b6(2)); % Amplitude of the second peak
Z(k)=PkTime (b6 (2)); % Time of the second peak
figure;
plot(t,(signal(k,:)),t,abs(hilbert(signal(k,:))),t(b2),a(k),'ro')
hold on
plot(PkTime, PkAmp, '^r', 'MarkerFaceColor','r')
xlim([0 0.0006]);ylim([-inf inf])
grid on;hold on
plot(Z(k),M(k),'ko')
hold off
end
Alex Mcaulley
Alex Mcaulley 2019-6-12
I don't understand what do you want exactly, but to extract the peaks you want you don't need to use the max function:
for k = 1: size (signal, 1)
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(k,:))),t);
[~,idx] = sort (PkAmp, 'descend' );
b(k) = idx(1); % Index of the largest peak
a(k) = PkAmp (b(k)); % Amplitude of the largest peak
time(k) = PkTime (b(k)); % Time of the largest peak
b2(k) = idx(2); % Index of the second largest peak
a2(k) = PkAmp(b2(k)); % Amplitude of the second largest peak
time2(k) = PkTime (b2(k)); % Time of the second largest peak
%Some plots
end
Jan
Jan 2019-6-12
Use maxk(Signal, 2) instead of sorting the complete vector.
Ramesh Bala
Ramesh Bala 2019-6-13
Thank you it works well.
I would like to know if there is a way to collect all the peak values in a matrix ?
for k = 1: size (signal, 1)
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(k,:))),t);
b2(k) = idx(2); % Index of the second largest peak
a2(k) = PkAmp(b2(k)); % Amplitude of the second largest peak
time2(k) = PkTime (b2(k)); % Time of the second largest peak
%this helps me to idenitfy largest peaks ,but how can I collect all the %peak values of a figure into a matrix??
end
Alex Mcaulley
Alex Mcaulley 2019-6-13
In fact, you have all the peaks in PkAmp variable and the time they occur in Pktime.
Ramesh Bala
Ramesh Bala 2019-6-13
Yeah you're right .But I can't group as it says " 1-by-85 and the size of the right side is 1-by-87."
for the obtained values
Ramesh Bala
Ramesh Bala 2019-6-13
[PkAmp(k,:), PkTime(k,:)] = findpeaks(abs(hilbert(signal(k,:))),t);
Ramesh Bala
Ramesh Bala 2019-6-13
The above one doesn't work as the matrix is changing its size.so,how to group such changing matrix
Alex Mcaulley
Alex Mcaulley 2019-6-13
Using cell array:
[PkAmp{k}, PkTime{k}] = findpeaks(abs(hilbert(signal(k,:))),t);
Ramesh Bala
Ramesh Bala 2019-8-6
Dear Alex
I have one more silly doubt in removing the index,I'm trying to find now the the largest time instead of Amp.So,I have used 'ascend' function which helps me to plot the the required time.
clc
clear all
close all
format long;
filenames={"30827"}
S(:,1) = [25 25 21.4 17.92 28.5 32.07 30 35 20 15];
S(:,2)= [10 15 8.5 12.07 8.5 12.07 5 5 5 5 ];
for i=1:numel(filenames)
s(i)=load (filenames{i});
signal(i,1:length(s(i).ans))=s(i).ans; % loading the signals from the scanning pts
end
load t.mat; %loading the time values
for k=1:1:length(S)
[a(k),b2]=max(abs(hilbert(signal(k,:)))); % first peak amp & index
%finding the peaks
set(0,'DefaultFigureWindowStyle','docked')
[PkAmp, PkTime] = findpeaks(abs(hilbert(signal(k,:))),t);
[~,idx] = sort (PkTime, 'ascend' );
b6(k) = idx(4); % Index of the fourth largest peak
a6(k) = PkAmp(b6(k)); % Amplitude of the fourth largest peak
time4(k)= PkTime (b6(k)); % Time of the fourth largest peak
figure;
plot(t,(signal(k,:)),t,abs(hilbert(signal(k,:))),t(b2),a(k),'ro')
hold on;grid on
plot(PkTime, PkAmp, '^r', 'MarkerFaceColor','r')
%plotting 4th largest
hold on,plot(time4(k), a6(k),'ko')
hold off
end
As per the script it plots the 4th largest PKTime peak .But how to remove other PkTime based on highest "a" highest PKAmp and then recontinue to plot the graph by taking highest(PKAMP) as PKTIME 1?

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更多回答（1 个）

Steven Lord
Steven Lord 2019-6-13

1 个投票

Use the islocalmax function with the 'MaxNumExtrema' option.

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