Passing numpy arrays to matlab

Andrew Straw strawman at
Wed Nov 8 10:57:44 CST 2006

David Cournapeau wrote:
> Andrew Straw wrote:
>> David Cournapeau wrote:
>>>     - To send data from the calling process to matlab, you first have to 
>>> create a mxArray, which is the basic matlab handler of a matlab array, 
>>> and populating it. Using mxArray is very ackward : you cannot create 
>>> mxArray from existing data, you have to copy data to them, etc... 
>> My understanding, never having done it, but from reading the docs, is
>> that you can create a "hybrid array" where you manage the memory. Thus,
>> you can create an mxArray from existing data. However, the docs
>> basically say that this is too hard for most mortals (and they may well
>> be right -- too painful for me, anyway)!
> Ok, I have looked at it. It is not hard, it is just totally brain 
> damaged: there is no way to destroy a mxArray without destroying the 
> data it is holding, even after a call with mxSetPr. So the data 
> referenced by the pointer given to mxSetPr is always destroyed by 
> mxDestroyArray; I don't see any way to use this to avoid copy... They 
> could at least have given a function which frees the data buffer and one 
> which destroys the other stuff; as it is, it is totally useless, unless 
> you don't mind memory leaks.
It does sound brain damaged, I agree. But here's a suggestion: can you
keep a pool of unused mxArrays rather than calling mxDestroyArray? I
guess without the payload, they're just a few bytes and shouldn't take
up that much space.

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