How to use global variable as local variable

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sneha bharadwaj 2017-1-9

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https://ww2.mathworks.cn/matlabcentral/answers/319613-how-to-use-global-variable-as-local-variable

编辑： Stephen23 2020-12-2

采纳的回答： Stephen23

I have global variables x,y and z i want to use it as local variables how can i use them?

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Stephen23 2020-12-2

https://web.archive.org/web/20201202181234/https://www.mathworks.com/matlabcentral/answers/319613-how-to-use-global-variable-as-local-variable

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Answer 1

Stephen23 2017-1-9

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https://ww2.mathworks.cn/matlabcentral/answers/319613-how-to-use-global-variable-as-local-variable#answer_249878

编辑：Stephen23 2017-1-9

在 MATLAB Online 中打开

"How to use global variable as local variable"

The best answer is "don't". Good code does not use globals: "I have never seen MATLAB code where globals were the right thing to do.... Most of the time I have seen globals being used it was a situation where the code author did not understand scoping of variables. Rather than pass variables from one function to another, they were just being made global."

http://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

If you really want to program using buggy methods (eg using globals), then declare them at the top of your function, exactly as the global documentation shows:

global X Y

Note that using globals is a bad programming practice that will make your code very hard to debug. Passing arguments is much more robust, and is the recommended way of passing data between workspaces:

http://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

https://www.mathworks.com/matlabcentral/answers/14857-where-do-people-learn-bad-programming-habits-i-e-goto-global-and-eval

https://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

https://www.mathworks.com/matlabcentral/answers/74626-how-to-declear-global-array-and-how-to-use-it

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Dan Bindman 2020-12-2

Oh yeah please explain to me what method you would use other than Global to deal with 20GB+

data matrices. Are you going to pass that in functions? Beause you are going to double (or more) the memory draw for every pass through! Or am I missing something?

Stephen23 2020-12-2

编辑：Stephen23 2020-12-2

"Oh yeah please explain to me what method you would use other than Global to deal with 20GB+ data matrices. Are you going to pass that in functions? Beause you are going to double (or more) the memory draw for every pass through! Or am I missing something?"

You might be missing an understanding of MATLAB's copy-on-write approach to data handling:

https://www.mathworks.com/help/matlab/matlab_prog/avoid-unnecessary-copies-of-data.html

Depending on the algorithm and if the code is carefully designed then it is certainly possible to write code that passes data to functions and does not make any copies of it in memory.

If the data are very large you should consider using tall arrays:

https://www.mathworks.com/help/matlab/tall-arrays.html

If you want any help or further advice on either of these then please ask a question and someone will help you with your specific use-case.

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