Plotting peaks and troughs of a large oscillating simulation data

Hi there,

I'm trying the create something that looks like this

Based on my data (the top subplot) I've managed to get the peaks (bottom subplot) using the following code

time_tot = d(:,1);                               
displacement= d(:,2);                                    

[Maxima,MaxIdx] = findpeaks(displacement);
time_max = time_tot([MaxIdx])

i=i+1 ;figure(i)
hold on
subplot(2,1,1)
plot(time_tot,displacement)
subplot(2,1,2)
plot(time_max,Maxima)
hold off

However, I'm not sure how to get the troughs. If anyone could help with this problem, then I would be greatly appreciative.

Best regards,

Lloyd

Answer 1

[Star Strider]

One option, if you are using findpeaks, is to negate it and then plot the negative of the peaks.

Example —

t = linspace(0, 250*pi, 10000);                             % Create Data
s = sin(t) .* cos(t/50);                                    % Create Data

figure
plot(t, s)

[pospks,posidx] = findpeaks(s);                             % Positive Peaks
[negpks,negidx] = findpeaks(-s);                            % Negative Peaks

figure
plot(t(posidx), pospks)
hold on
plot(t(negidx), -negpks)
hold off

[Lloyd Sullivan]

Works perfectly - Thank you so much for replying within minutes Star Strider!

cheers,

Lloyd

[Star Strider]

As always, my pleasure!