The NumPy Fortran-ordering quiz

Charles R Harris charlesr.harris at gmail.com
Wed Oct 18 13:08:07 CDT 2006


On 10/18/06, Tim Hochberg <tim.hochberg at ieee.org> wrote:
>
> Charles R Harris wrote:
>
> [SNIP]
> >
> > I'm not talking about the keyword in the ravel call, I'm talking about
> > the flag in a. The question is: do we *need* a fortran flag. I am
> > argueing not, because the only need is for fortran contiguous arrays
> > to pass to fortran function, or translation from fortran contiguous
> > arrays to numpy arrays. What I am saying is that things are
> > unnecessarily complicated. None of the LaPack stuff seems to use the
> > Fortran stuff, they just transpose and copy. I don't even think I want
> > to change that, because it is *clear* what is going on. Interfacing to
> > fortran is all about memory layout, nothing more or less.
> >
>
> Chuck,
>
> There are two things here. One is the order keyword and one is the
> FORTRAN flag. The latter is mainly an optimization for use at the
> C-level so that one doesn't have to check whether a given array is in
> contiguous FORTRAN order by examining the strides, in the same way that
> the CONTIGUOUS flag allows you to skip examining the strides when you
> need a contiguous C-order matrix.


That sounds like the two flags should be named f-contiguous and
c-contiguous. Then they would be orthogonal and one could have all four
combinations. Is that the case now? Perhaps I am misunderstanding the
meaning of the flags.


I believe it is the former that you
> are objecting to, but it would help if you could specify whether you are
> talking about the order keyword or whether you are talking about the
> FORTRAN flag.


Both. I was argueing against the FORTRAN flag, and of limiting the order
keyword to those cases where f or c contiguous arrays were the output or
input.

I'll also note that the order keyword could probably have been used to
> fix a performance problem someone was having a few weeks ago. We ended
> up transposing the data, but the individual felt that obscured the
> intent of the algorithm. I believe the same effect could probably have
> been been achieved without re jiggering the algorithm by using the order
> parameter.


Some more details would be helpful. It would be good to know what problem
the order keyword should solve.

Chuck
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