Finding local minima and maxima

Hi,

i have been trying find a way of plotting the local maxima and local minima.

I have used the findpeaks(); fuinction for the both of them, but it gives me two signals being plotted, i belive this will be because the singal has been negatively multiplied to try to find the local minima.

However i am trying to plot both max and min onto the same singnal, and the markers to be of diffenet colour.

Below is the code that i have tried to use, ive inlcuded a seperate way of finding local minima, but i am unsure of how to plot this on the same singal.

t = (0:100)*0.6*10^-3;
x1 = 3*sin(2*pi*100*t);
findpeaks(x1);
hold on
findpeaks(-x1);
%TF = islocalmin(x1);
%plot(t,x1,t(TF),x1(TF),'r*')

Answer 1

[Star Strider]

You already found the correct functions. Applying them appropriately appears to be the problem.

Try this:

t = (0:100)*0.6*10^-3;
x1 = 3*sin(2*pi*100*t);

TFmax = islocalmax(x1);
TFmin = islocalmin(x1);

figure
plot(t, x1)
hold on
plot(t(TFmax), x1(TFmax), '^r', 'MarkerFaceColor','r')
plot(t(TFmin), x1(TFmin), 'vg', 'MarkerFaceColor','g')
hold off
grid

.

[Samuel Courtney]

Hi,

Thanks for the great suggestion.

is there any way of using the findpeaks fucntion for this ??

[Star Strider]

My pleasure!

To use findpeaks requires a bit of creativity.

[pks,plocs] = findpeaks(x1);
[vlys,vlocs] = findpeaks(-x1);

figure
plot(t, x1, '-b')
hold on
plot(t(plocs), pks, '^r', 'MarkerFaceColor','r')
plot(t(vlocs), -vlys, 'vg', 'MarkerFaceColor','g')
hold off
grid

Producing essentially the same plot.