To find the first 3 local maximas of a plot/ dataset without the islocalmax and findpeaks

Hi, everyone

Is it possible to find the first 3 local maximas of a plot/ dataset without the islocalmax and findpeaks syntax?

Thanks in advance, Grace

Answer 1

[Star Strider]

Yes.

Is this for homework or an exam?

[GH]

None of that, I am practicing MatLab by my own, I made up a task which includes this part.

I have the 'lmax' from the file exchange which can find local maximas, and filter them by their neighbours. So I was thinking I should list the found lmax datas from biggest to smallest and there I go, but I questioned myself, about the effectiveness of my solution, that's why I asked.

[Star Strider]

O.K.

Try this:

t = [1:0.01:5];                                                         % Time Vector
y = sin(2*pi*t);                                                        % Signal
dydt = gradient(y, mean(diff(t)));                                      % Derivative
zci = @(v) find(diff(sign(v)));                                         % Define Function
zx = zci(dydt);                                                         % Zero Crossings
[max1,idx] = maxk(y(zx),3);                                             % First Three Maxima & Indices
Out = [t(zx(idx)); y(zx(idx))];                                         % Result Matrix

figure
plot(t, y, '-b')
hold on
plot(Out(1,:), Out(2,:), 'r^')
hold off
grid

.

[GH]

Thanks a lot! (:

[Star Strider]

As always, my pleasure!