how to retain a variable in memory in mex function after its execution
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Hi everybody,
I want to use a mex fucntion in Matlab. My requirement is that i have a matrix in Matlab that should be processed by a mex function using different arguments generated in loop in Matlab. In order to save execution time i do not want to pass the matrix to the mex function in every loop as the matrix is very large.
Is it possible to transfer the matrix for once to a fixed location in memory, so that the mex function can access it during every execution and is retained at the same location even after the call to the mex function.
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Matt J
on 11 May 2014
Edited: Matt J
on 11 May 2014
Is it possible to transfer the matrix for once to a fixed location in memory, so that the mex function can access it during every execution and is retained at the same location even after the call to the mex function.
There is never any transfer of matrix data when you call a mex. When you send a matrix to a mex function, you are not passing it by value, i.e., copying all of its data to a separate workspace. The mex gateway function receives an mxArray pointer which points to where the data already resides in the MATLAB workspace. And it is that data that gets used as input.
Now it is possible that time is consumed when fresh memory is allocated for the output of the computations, but that is at the discretion of the author of the mex file. He/she can put the result anywhere desired, either in freshly allocated memory or in space already occupied by existing matrices.
4 Comments
Jan
on 11 May 2014
No, do not do this! Never overwrite data of an input variable. The variable could contain shared data and you would destroy the internal logic.
Matt J
on 11 May 2014
In general, I'd agree with that, Jan. But in this instance things are well-controlled. We know that the input variable will not be shared.
More Answers (1)
Jan
on 11 May 2014
You can use mxMakeMemoryPersistent or mxMakeArrayPersistent as well as the usual static property of C-variables.
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