[Numpy-discussion] Fortran order arrays to and from numpy arrays

Alexander Schmolck a.schmolck@gmx....
Sat Feb 24 19:44:01 CST 2007


"Charles R Harris" <charlesr.harris@gmail.com> writes:

> > Unfortunately I don't see an easy way to use the same approach the other
> > way
> > (matlab doesn't seem to offer much on the C level to manipulate arrays),
> > so
> > I'd presumably need something like:
> >
> >   stuff_into_matlab_array(a.T.reshape(a.shape).copy())
> >
> > the question is how to avoid doing two copies.
> >
> > Any comments appreciated,
> 
> 
> The easiest way to deal with the ordering is to use the order keyword in
> numpy:
> 
> In [4]: a = array([0,1,2,3]).reshape((2,2), order='F')
> 
> In [5]: a
> Out[5]:
> array([[0, 2],
>        [1, 3]])
> 
> You would still need to get access to something to reshape, shared memory or
> something, but the key is that you don't have to reorder the elements, you
> just need the correct strides and offsets to address the elements in Fortran
> order. I have no idea if this works in numeric.

It doesn't work in Numeric, but that isn't much of any issue because I think
it ought to be pretty much equivalent by transposing and reshaping. However
the problem is that I *do* need to reorder the elements for numpy->matlab and
I'm not sure how to best do this (without unnecessary copying and temporary
numpy array creation but using numpy functionality if possible).

'as


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