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

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Vish 2016-2-3

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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 2017-4-4

在 MATLAB Online 中打开

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 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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Answer 1

Image Analyst 2016-2-3

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https://ww2.mathworks.cn/matlabcentral/answers/266481-how-can-i-give-variable-name-having-2-number-of-nested-loop-i-and-j#answer_208439

在 MATLAB Online 中打开

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.