How to includ/plot the local maxima date on a plot?

Hi everyone, I have defined the following and it shows the date values intractively (mytime) on the plot, but I want to actually plot them on the figure so that I can export it as jpeg. Also, how can I highlight them with triangles as the normal findpeaks does?

[pks,locs] = findpeaks(Data,'MinPeakProminence',2)
x_peaks = Mytime(locs)
plot(Mytime,Data,  x_peaks,pks,'pg')

Answer 1

[Suraj Kumar]

Hi Wolfgang,

From what I understand you want to plot the local maxima, annotate them with their corresponding dates and highlight these maxima using triangles.

You can use "findpeaks" functon to identify the local maxima in your data. Then you can plot the entire dataset to provide context and use "plot" function to overlay the triangles at peak locations to highlight them.You can refer to the attached code snippets with sample data for better understanding:

Data = [1, 3, 7, 1, 2, 6, 0, 1, 3, 2, 5, 1];
Mytime = datetime(2023,10,1) + days(0:length(Data)-1);
[pks, locs] = findpeaks(Data, 'MinPeakProminence', 2);
x_peaks = Mytime(locs);
plot(Mytime, Data, '-b'); 
hold on; 
plot(x_peaks, pks, '^r', 'MarkerFaceColor', 'r');

Then you can use the "text" function to annotate each peak with corresponding date and use the "saveas" function to export the plot as a JPEG image.

for i = 1:length(locs)
    text(x_peaks(i), pks(i), datestr(x_peaks(i), 'mm/dd'), 'VerticalAlignment', 'bottom', 'HorizontalAlignment', 'right');
end
xlabel('Date');
ylabel('Data Value');
title('Data with Local Maxima Highlighted');
datetick('x', 'mmm dd', 'keepticks'); 
saveas(gcf, 'plot_with_peaks.jpg');
hold off;

To learn more about the functions used above, you can refer to the following documentation links:

findpeaks: https://www.mathworks.com/help/signal/ref/findpeaks.html

plot: https://www.mathworks.com/help/matlab/ref/plot.html

text: https://www.mathworks.com/help/matlab/ref/text.html

saveas: https://www.mathworks.com/help/matlab/ref/saveas.html

Happy Coding!