Passing numpy arrays to matlab
Andrew Straw
strawman at astraw.com
Tue Nov 7 00:49:36 EST 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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