Executing one function slows down built-in functions in another independent function

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Tien-Ju Yang 2016-6-3

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https://ww2.mathworks.cn/matlabcentral/answers/287151-executing-one-function-slows-down-built-in-functions-in-another-independent-function

关闭： MATLAB Answer Bot 2021-8-20

Hi,

I encounter a strange speed problem. The problem is that executing one function slows down built-in functions in another independent function. Assume there are two functions, funcA() and funcB(). When I execute only funcB(), it takes 10 seconds. When I execute first funcA() and then funcB(), funcB() now takes 50 seconds. Moreover, if I first type "funcA()" in the command window and run it, and then type "funcB()" in the command window and run it, funcB() takes only 10 seconds. If I write a script as the following: " funcA(); funcB(); " and run this script, funcB() takes 50 seconds. I tried to insert "clear", "clear all" in between. funcB() still takes 50 seconds.

I used "profile" to find what is the part causing the slow down. It turns out some built-in functions become much slower, such as "max" and "bsxfun".

funcA() and funcB() uses different inputs and have no output. I also used breakpoints to check the I/Os of the slow built-in functions. The I/Os are exactly the same across all experiments.

I also used "top" to check the memory usage, but in all experiments I have a lot of free memory.

Does anyone have an idea about what is going on or how to debug this?

Thanks!

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Matt J 2016-6-3

编辑：Matt J 2016-6-3

Were any of these tests done inside a function mfile as opposed to the command line or scripts? It's important to test that because the JIT is only active inside mfunctions, I believe.