how can i give variable name having 2 number of nested loop(i and j) ?

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Vish
Vish 2016-2-3
编辑： Stephen23 2019-6-19
for i=1:3
for j=1:3
im(i,j)=%action;
end
end
while doing same above code i get error as: "Undefined function or variable 'im'." and warning as: "The Variable 'im' appears to change size on every loop iteration. consider preallocating for speed" here my im variable must b im11,im12,im13,im21....im33 how can i give such variable name in matlab
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Akbar Khan
Akbar Khan 2017-4-4
It is a good idea to initialize a variable before loop to avoid any warning .. however you code will not result in any error during compilation or execution. However is is always a good c programming practice to initialize variables before loops like
im = zeros(3, 3);
Stephen23
Stephen23 2017-4-4
编辑：Stephen23 2019-6-19
"...is always a good c programming practice..."
But this is MATLAB, not C. There is no reason why any "good programming practice" in language X has to be good in language Y.
https://www.mathworks.com/matlabcentral/answers/31248-variable-declaration-in-matlab
MATLAB does not require initializing of variables. However preallocating variables is recommended before loops:
https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html
"...variable must b im11,im12,im13,im21....im33 how can i give such variable name in matlab"
Don't do this. Use indexing.
https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

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回答（1 个）

Image Analyst
Image Analyst 2016-2-3
Don't worry about the warning but don't give unique names to the variables like im11, im12, im13, etc. For more discussion about this bad idea, see the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F
If you want to get rid of the warning, preallocation im with
im = ones(3,3);
before the loop.

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