problem of using findpeaks

I have two vectors of time (datetime formate) and elevation, but there is an error to use findpeaks(elev,time), saying "Expected X to be strictly increasing."

Answer 1

[Star Strider]

My guess is that the datetime values are not considered to be monotonically increasing because they span multiple years.

Try this as a work-around —

LD = load('19year.mat');
elev = LD.elev;
timing = LD.timing;

[pks,plocs] = findpeaks(elev);
[vys,vlocs] = findpeaks(-elev);

figure
plot(timing, elev, 'DisplayName','Data')
hold on
plot(timing(plocs), pks, '^r', 'MarkerSize',2.5, 'DisplayName','Peaks')
plot(timing(vlocs), -vys, 'vg', 'MarkerSize',2.5, 'DisplayName','Valleys')
hold off
grid
xlabel('timing')
ylabel('elev')
legend('Location','best')

figure
plot(timing, elev, 'DisplayName','Data')
hold on
plot(timing(plocs), pks, '^r', 'DisplayName','Peaks')
plot(timing(vlocs), -vys, 'vg', 'DisplayName','Valleys')
hold off
grid
xlabel('timing')
ylabel('elev')
legend('Location','best')
xlim([timing(1)  timing(500)])

.

Answer 2

[Chunru]

load(websave("19year.mat", "https://www.mathworks.com/matlabcentral/answers/uploaded_files/1553817/19year.mat"))
% It seems that timing contains duplcate data.
% fild peaks require x-axis to be monotonically increasing.

% Workaround:
% sort the data
[timing, i] = sort(timing);
elev = elev(i);

% find the peaks and location
[pks, locs] = findpeaks(elev, MinPeakProminence=1);
plot(timing, elev);
hold on
plot(timing(locs), pks, 'rv', 'Markersize', 5)