MATLAB: The same function is taking more time after MEX creation

MATLABmatlab codermexmex compiler

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??

Best Answer

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.
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