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how to draw a peak line

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Luca Re
Luca Re on 28 Sep 2024
Commented: Star Strider on 29 Sep 2024
Hi, i've data and i want to draw a line that corresponds to the peaks (where there is a zero the previous value >0 must be pasted) (See black line painted)
Is there a function or graph type that does this to me?

Accepted Answer

Star Strider
Star Strider on 29 Sep 2024
If you have the Signal Processing Toolbox, use the findpeaks function with an approopriate valuee for 'MinPeakProminence' so that it only detects certain peaks —
date = datetime(2022,01,01) : caldays(1) : datetime(2024,9,28);
t = day(date,'dayofyear');
data = cos(2*pi*t/28).*cos(2*pi*t/7)/10+rand(size(date))/10;
[pks,locs] = findpeaks(data, 'MinPeakProminence',0.15);
figure
plot(date, data, '-r','LineWidth',2)
hold on
plot(date(locs), pks, '-k', 'LineWidth',1)
hold off
grid
xlim('tight')
ylim([0 max(ylim)])
You will have to experiment wiith the 'MinPeakProminience' value. A good guess for a starting value is approximately half way between the shortest and tallest peaks, then adjust it as necessary.
It would be helpful to have your data.
  2 Comments
Luca Re
Luca Re on 29 Sep 2024
thank you but i don't have this toolbox
Star Strider
Star Strider on 29 Sep 2024
My pleeasure!
O.K. Instead use:
Lvmn = islocalmax(data, 'MinProminence',0.15);
Changing my previous code to accommodate it —
date = datetime(2022,01,01) : caldays(1) : datetime(2024,9,28);
t = day(date,'dayofyear');
data = cos(2*pi*t/28).*cos(2*pi*t/7)/10+rand(size(date))/10;
Lvmn = islocalmax(data, 'MinProminence',0.15); % Returns Logical Veector
locs = find(Lvmn); % Not Specifically Necessary, Returns Numeric Indices Of Peaks
pks = data(Lvmn); % Necessary, Returns Peak Amplitude Values
figure
plot(date, data, '-r','LineWidth',2)
hold on
plot(date(locs), pks, '-k', 'LineWidth',1)
hold off
grid
xlim('tight')
ylim([0 max(ylim)])
Again, it may be necessary to experiment with the 'MinProminence' value to get the reesult you want.
.

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More Answers (1)

Walter Roberson
Walter Roberson on 29 Sep 2024
mask = islocalmaximum(YourSignal);
peak_times = YourSignalTimes(mask);
peak_values = YourSignal(mask);
plot(peak_times, peak_values);

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