Protect the size of a preallocated matrix

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Martijn Kortenhoeven 2020-2-22

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评论： Martijn Kortenhoeven 2020-2-22

I am trying to protect the preallocated size of a matrix, to avoid making mistakes, and getting/giving an error when the matrix size changes, without having to check the size everytime I do an iteration. Consider the following code.

>> A = zeros(2,2);
>> A(1,3) = 5
A =
     0     0     5
     0     0     0
     

I am aware I can check the size of the matrix everytime I change it. I am wondering however, whether Matlab can give me an error/warning, since you do get a warning with the following code:

A = [];
for i = 0:5
    A = [A;eye(2)];
end % Warning: The variable A appears to change size at every iteration. Consider preallocating for speed.

If Matlab could give an error, I would preferably get this in the command window.

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Answer 1

Giuseppe Inghilterra 2020-2-22

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Hi,

in MATLAB numeric arrays are free to change size, i.e. if you add an element outside intial defined dimension, then array will be extended and no warning/error is shown.

You can define a user defined class (with a object oriented programming approach) in order to fix dimension of your numeric arrays. Otherwise you should check frequently size of your array and show a custom message on command window (by usind disp function) if size changes along code (but it is not a real solution).