# How to do matrix Preallocation?

2 vues (au cours des 30 derniers jours)
Hannah le 18 Août 2021
Modifié(e) : Stephen23 le 18 Août 2021
I have a matrix called 'ResultMtx'. its size is
size(ResultMtx)
ans =
792 5
I try to do Preallocation of the matrix by writing:
ResultMtx = zeros(792,5);
Then later in my program I calculate values for the matrix and define it like this:
ResultMtx = [ResultMtx; m, o, r, t, Diff_irr];
end
ResultMtx = [ResultMtx; nan nan nan nan nan];
But then the result of my matrix is all zeros. what am i doing wrong?
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### Réponses (1)

Stephen23 le 18 Août 2021
Modifié(e) : Stephen23 le 18 Août 2021
"what am i doing wrong?"
You are concatenating the new data onto the bottom of your preallocated matrix, rather than using indexing to allocate that data to the matrix. You need to use indexing, for example where k is the loop iteration:
ResultMtx(k,:) = [m,o,r,t,Diff_irr];
% ^^^^^ indexing!
or
ResultMtx(k,:) = NaN;
% ^^^^^ indexing!
This approach is shown in the documentation:
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