Problem with findpeaks 3D grid

Hey all,

I have a velocity values over 720 time steps for a curvilinear grid (40x144x720). I would like to obtain the peak in all the grid points. One problem that I have is that the number of peaks are different in all the points.

I tried using the function findpeaks, and if I discretize one point, it works well. My problems is when I try the loops and I don´t know really well I storage the output.

u_atl=squeeze(u(:,:,1,:));%size(40x144x720)
n=720; %time steps
i=zeros(40,144);%latitud and longitud
j=zeros(40,144);
for i=1:40
    for j=1:144
        for k=1:n
            [pval(i,j,k),ploc(i,j,k)]=findpeaks(u_atl(i,j,k),'minpeakdistance',6);
            [peak_ebb(i,j,k),ploc(i,j,k)]=findpeaks(-u_atl(i,j,k),'minpeakdistance',6);
        end 
    end
end

I'm pretty new in Matlab so I hope you can help me.

Thanks in advice,

Miguel.

Answer 1

[Ameer Hamza]

findpeaks() needs a vector, whereas you are passing it a scalar. It will not work properly. Also, if the number of peaks is different, then you will need to use a cell array to store all values. Normal arrays can only hold values when all the dimensions are of the same length. Try something like this

u_atl=squeeze(u(:,:,1,:));%size(40x144x720)
pval = cell(40, 144);
ploc = cell(40, 144);
peak_ebb = cell(40, 144);
ploc_ebb = cell(40, 144);
for i=1:40
    for j=1:144
        [pval{i,j},ploc{i,j}] = findpeaks(squeeze(u_atl(i,j,:)), 'minpeakdistance', 6);
        [peak_ebb{i,j},ploc_ebb{i,j}] = findpeaks(-squeeze(u_atl(i,j,:)), 'minpeakdistance', 6);
    end
end

[Miguel andres]

Hi,

I tried that and yeah, the error that appear is that findpeaks spect to use a vector.

But I don't understand why when I discretize one point it works. The loops should select point after point.

I attach here the values that I want for a selected point. Maybe you have another idea how to obtain them in all the points.

Thank you really much again.

[Ameer Hamza]

Is this one signal from the 40x144x720 matrix? Do you get an error when you run my code?

[Miguel andres]

This signal is if I do A=squeeze(u_atl(25,25,:)). So A is 720x1.

If I do [value,location]=findpeaks(A) it works. The plot is:

plot(A)

hold on

scatter(location,value)

The problem iswhen I have to do the loops, something is wrong but I don´t know what.

Thank you.

[Ameer Hamza]

Try the updated code in my answer. There was a mistake.

[Miguel andres]

Yeah, seems that it works!!

Thank you really much.

[Ameer Hamza]

I am glad to be of help.