How to find troughs of a signal below a threshold

I am trying to find troughs of a signal which are below a certain threshold

I tried findpeaks but its not working

findpeaks(-1*TrialLFP{1,iSession}(chan,:),'Threshold',sigma);

Is there any thresholding option for islocalmin function?

[Jan]

What are "throughs of a signal"? What does "is not working" mean explicitly?

Answer 1

[Star Strider]

Use the 'MinPeakHeight' name-value pair —

t = linspace(0, 2*pi, 500);
s = sin(2*pi*t) - sin(2*pi*0.1*t-0.45);

Threshold = -1.75;

[pks,locs] = findpeaks(-s, 'MinPeakHeight',-Threshold)

pks = 1×2

1.9576 1.9443

locs = 1×2

220 298

figure
plot(t, s)
hold on
plot(t(locs), s(locs), 'vr', 'MarkerFaceColor','r')
hold off
grid
ylim([-2.5 1.5])
yline(Threshold, '--m', 'Threshold')

.