The NumPy Fortran-ordering quiz

George Nurser gnurser at googlemail.com
Wed Oct 18 17:21:19 CDT 2006


On 18/10/06, Charles R Harris <charlesr.harris at gmail.com> wrote:
>
>
> On 10/18/06, George Nurser <gnurser at googlemail.com> wrote:
> > > > None of the LaPack stuff seems to use the Fortran stuff, they just
> > > > transpose and copy.
> >
> > You've got me worried here. I have assumed that when you start with a
> > c-contiguous array, a, with say, a.shape = (m,n), if you use the
> > transpose as an argument to a fortran routine which requires an mxn
> > size array, then no copying is required.
> >
> > This seems to work for me -- the transpose *does* have fortran order.
>
> Nope. The result is an (n,m) array in fortran order, not an (m,n) array in
> fortran order.

Presumably that's because it's a view of the original array.

>> > Also, in f2py, if I use -DF2PY_REPORT_ON_ARRAY_COPY=1 I receive no
> > alert of any copy.
>
> f2py takes care of the ordering, which is one reason why it is so useful.

Yes, when I first used it, I assumed that the fortran routine had to
use an nxm array. But f2py is clever enough to make the above work.

George.

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