which one is faster? defining a variable as a global variable or as an input of function?
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I want to know which one is faster? defining a variable as a global variable or as an input of function?
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Accepted Answer
Walter Roberson
on 24 Aug 2015
global is slower. The location of the global variable must be searched at execution time when the "global" is encountered. The location of passed parameters is already known.
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Diaa
on 24 Jun 2021
Edited: Diaa
on 24 Jun 2021
Is it faster to define auxiliary variables instead of retrieving values from a parent matrix?
In other words, which one is faster:
a = randn(3,4);
clear b c d g
tic
b = a(3,4);
c = 5*b; d = 10*b; g = 20*b;
toc
clear c d g
tic
c = 5*a(3,4); d = 10*a(3,4); g = 20*a(3,4);
toc
knowing that my R2021a version tells me the second way is faster despite indexing into variable a multiple times?
More Answers (1)
David Young
on 23 Aug 2015
Edited: David Young
on 23 Aug 2015
It is usually a bad idea to use global variables. There are many papers, going back over 40 years or more, explaining why. One example is this chapter. I strongly recommend you avoid them. (Global variables, that is, not the papers.)
It is very unlikely that using a global rather than passing an argument will make a noticeable difference to your execution time. If you really suspect it might, the best way to find out is to do some tests using timeit.
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