How to remove rest of the rows of a Column once it reaches a certain value

I have an autocorrelation function that needs to be integrated only up to where the time threshold first drops below Zero.

So I have a matrix such as A = [ 1 2 7 -2 0 2 9 1 2 0 9 -5].

I want to get A1 = [ 1 2 7 ].

How can I do this?

Answer 1

[Walter Roberson]

AZ = A(find(~A,1)-1)

However, find can be a bit heavy. Sometimes it can be faster to do

AZ = A(1:sum(cumprod(logical(A))))

This processes the entire vector multiple times, but sometimes it can be better than find. Especially if you have a 2D array that you want to do this kind of selection for on a per-row or per-column basis.

[Avik Mahata]

Thanks a lot for the reply. I just tried the second command and its giving me

AZ =[ 1 2 7 -2]

I wanted get AZ =[ 1 2 7]

[Walter Roberson]

AZ = A(1:sum(cumprod(A>0)))