Passing numpy arrays to matlab

Josh Marshall josh.p.marshall at gmail.com
Mon Nov 6 22:59:25 CST 2006


Hi David,

Did you have a look at mlabwrap? It's quite hard to find on the net,  
which is a shame, since it is a much more up to date version,  
enhancing pymat with the things that you are trying to do. It allows  
passing arrays and getting arrays back.

http://mlabwrap.sourceforge.net/

However, I do agree with you that it would be good to have a bridge  
based on ctypes. I can't really help since I long ago moved all of my  
code from Matlab to Numpy and Matplotlib.

Cheers,
Josh M

David Cournapeau <david at ar.media.kyoto-u.ac.jp> wrote:
>
> Hi,
>
>     I am trying to find a nice way to communicate between matlab and
> python. I am aware of pymat, which does that, but the code is
> deprecated, and I thing basing the code on ctypes would lead to much
> more robust code.
>
>     http://claymore.engineer.gvsu.edu/%7Esteriana/Software/pymat.html
>
> I have a really simple prototype which can send and get back data from
> matlab, but I was wondering if it would be possible to use a scheme
> similar to ctypes instead of having to convert it by hand. Let me
> present the way communication with matlab is done:
>
>     - open a matlab session, which on unix launch a matlab process,  
> and
> set up pipes between the calling process and matlab process for
> communication
>     - 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...  
> (it is
> one of the reason I started looking in python in the first place:
> interfacing matlab with foreign code is really not a nice experience,
> and the API is not rich enough to do many interesting things; I am
> actually amazed how poor this part of matlab is, a product which is  
> now
> 20 years old).
>
>     I was wondering if there was a way to extend a numpy array so  
> that I
> could send directly numpy arrays to matlab C functions expecting a ,
> with ctypes doing the hard work. For example, now, to send data to
> matlab, I do:
>
>     session   = MatlabEngine()
>     # data is a numpy array, 'dataname' a string with its name inside
> matlab interpreter
>     session.put(data, 'dataname')
>
> The put function has do to a lot for work:
>     - first, getting metadata from data (dimensions, real or complex,
> etc...)
>     - then creating a mxArray with the same metadata
>     - then populating the mxarray by copying the data from the  
> numpy array.
>
> And of course, taking care that all mxarrays are detroyed, otherwise,
> memory leak... That's why I was thinking about something a bit  
> smarter:
> creating a mxarray class which implements the numpy interface. I could
> create a mxarray from a numpy array easily, send a mxarray directly  
> to C
> function with ctypes, etc... Is this doable ? Would this take care of
> correct destruction of mxarrays ? I really don't know much about the
> internals of numpy arrays, so I don't really know how to start,
>
>     cheers,
>
>     David
>
>


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