Passing numpy arrays to matlab

Andrew Straw strawman at astraw.com
Mon Nov 6 23:49:36 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)!
>>   
>>     
> Would you mind telling me where you found that information ? Because 
> right now, I am wasting a lot of cycles because of memory copy in both 
> directions, and it is sometimes slow enough so that it is annoying,
>   
I found it reading through the in-program help (the C-API section,
whatever it's called) on a Matlab installation at my university. I guess
this was Matlab 2006A. A quick Google search turns this up:

http://www.mathworks.com/access/helpdesk/help/techdoc/matlab_external/index.html?/access/helpdesk/help/techdoc/matlab_external/f25255.html

They give the following example, which seems to create a Matlab array
"pArray" with data owned by the C variable "data":

mxArray *pArray = mxCreateDoubleMatrix(0, 0, mxREAL);
double data[10];

mxSetPr(pArray, data);
mxSetM(pArray, 1);
mxSetN(pArray, 10);


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