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Different speed of execution of the same code in different versions Matlab. 2014b and 2017a

조회 수: 24(최근 30일)
Nickolay Ternovoy
Nickolay Ternovoy 2018년 6월 3일
댓글: Walter Roberson 2018년 6월 4일
Hello. The question is this. Why are the same code executed at different speeds in different versions of matlab? Versions 2014b and 2017a.
Below are screenshots with the difference in code execution in different versions.
I noticed one strange thing. If I write code without declaring a function, then the difference in execution between versions is huge.
If the code is described as a function, then speed is greatly increased
code without declaring a function:
clear
b = rand(1000000,10);
i=1;
tic
while i <= 1000
res = b(:,1).*b(:,10);
i = i+1;
end
toc
result Matlab 2014b :
Elapsed time is 1.962136 seconds.
result Matlab 2017a :
Elapsed time is 8.741258 seconds.
code with function:
function f=Untitled
clear
b = rand(1000000,10);
i=1;
tic
while i <= 1000
res = b(:,1).*b(:,10);
i = i+1;
end
toc
end
result Matlab 2014b :
Elapsed time is 1.757147 seconds.
result Matlab 2017a :
Elapsed time is 1.885382 seconds.
p.s. Untitled is the name of the script / function
  댓글 수: 6
Rik
Rik 2018년 6월 4일
@Stephen, I was already corrected by Walter. I misspoke because I only use scripts in the base workspace for debugging, so for all my use cases it is in fact the base workspace. But, yes, you are correct, it's not actually the base workspace necessarily, but the workspace of the calling function.

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채택된 답변

Philip Borghesani
Philip Borghesani 2018년 6월 4일
This feels like a bug to me and I filed a bug report. Walter is correct that coding this as a function is expected to produce faster code but there is no reason for this big a performance difference.
If you can't easily convert your code to a function I suggest posting more information about the problem you are trying to solve with actual code, or creating a support call for the best solutions to this performance issue.
  댓글 수: 3
Walter Roberson
Walter Roberson 2018년 6월 4일
Philip is staff, and has filed a bug report about it already.

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추가 답변(1개)

Walter Roberson
Walter Roberson 2018년 6월 3일
The Just In Time engine historically compiled functions more than it compiled scripts. This had to do with the fact that scripts were more free to "poof" variables into existence, so decisions involving variables that might be set in a script call had to be made at run time, whereas static analysis for functions could be more thorough.
In R2015b a new Execution Engine started making more assumptions about what was happening in scripts, and started declaring that some potential changes in scripts would no longer be paid attention to or would now be errors. As a result, performance of code that included scripts improved.
  댓글 수: 2
Walter Roberson
Walter Roberson 2018년 6월 4일
Ah, yes, I am able to replicate the script slowdown for that code between R2014a and R2018a.

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