Why the same function is taking more time after MEX creation?

Question

JAI PRAKASH 2018-8-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/416421-why-the-same-function-is-taking-more-time-after-mex-creation

编辑： Ryan Livingston 2018-8-29

采纳的回答： Ryan Livingston

在 MATLAB Online 中打开

I want to create mex of 'sort()' funtion.

So I build below function

function idx = sort2(h)  % h is 600x1280 'single' elements
[~,idx] = sort(h(:));  % because I just want indices only, I dont want the elements.
end

If I call above funtion:

Why the 'MEX' is taking more time??

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Answer 1

Ryan Livingston 2018-8-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/416421-why-the-same-function-is-taking-more-time-after-mex-creation#answer_334395

编辑：Ryan Livingston 2018-8-29

The MATLAB Coder documentation has a section covering acclerating MATLAB code via MEX generation:

https://www.mathworks.com/help/coder/matlab-algorithm-acceleration.html

One page that's relevant to what you are seeing is:

https://www.mathworks.com/help/coder/ug/best-practices-for-using-mex-functions-to-accelerate-matlab-algorithms.html#bty93o_

It contains the statement:

Use MEX functions to accelerate MATLAB code only if user-generated code dominates the run time.

Avoid generating MEX functions if computationally intensive, built-in MATLAB functions dominate the run time. These functions are pre-compiled and optimized, so the MATLAB code is not accelerated significantly using a MEX function.

In MATLAB, sort is a built-in function that is hand-optimized and compiled. So the generated code likely won't be any faster and can be slower in some cases.