Finding specific data for a given condition

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gps
gps 2021-6-7
评论： KSSV 2021-6-7
I have this data set for which column 1 is time and column 2 is the number of atoms, and I'm trying to find variable N, which contains data that start at t>=0. I have done this:
index = find(Data >= 0, 1, 'first');
Ndecay = Data(index:end);
but I only get a row of data that corresponds to the time, rather than two rows, which should correspond to both time and number of atoms. How can I find the number of atoms corresponding to times at t>=0?

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回答（1 个）

KSSV
KSSV 2021-6-7
编辑：KSSV 2021-6-7
Let data be your m*2 array. To get number of atoms at t = 0, you can use interp1.
t = data(:,1) ; % time
N = data(:,2) ; % Number of atoms
ti = 0 ; % N is required here
Ni = interp1(t,N,ti)
[ti Ni]
If you want to use find and index.
idx = t==0 ;
data(idx,:)
  2 个评论
gps
gps 2021-6-7
编辑：gps 2021-6-7
@KSSV when I use this, I just get [0, 1121600], which is correct, but how can I find all the values for when t >= 0? So, I would have a matrix of values corresponding to t>=0 and the respective number of atoms at each time

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