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How to quickly save a matrix by adding rows?

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Benson Gou
Benson Gou on 22 Jun 2021
Commented: Stephen on 22 Jun 2021
Dear All,
I calculate a row Ai and save it in my defined matrix A using the following way:
A = [A; Ai];
But I foud it took a lot of time. Is there a faster way?
Thanks a lot.
Benson

Accepted Answer

dpb
dpb on 22 Jun 2021
Yes. Preallocate the array and index into it...without context it's conjecture what you have/are doing, but the general idea is
A=zeros(max(variable_i),size(A,2)); % preallocate A as array of zeros
for i=1:max(variable_i) % for the loop size each i
% whatever to compute Ai
...
A(i,:) = Ai; % store the new row in A
end
The above will not show degradation in speed as i increases.

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