On 10/17/06, A. M. Archibald <[EMAIL PROTECTED]> wrote:
So what is the point of having a fortran layout if things are not actually layed out in fortran order? As far as I can see, memory layout is the only reason for fortran ordering. Now I can sort of see where the fortran ravel comes from, because the result can be passed to a fortran routine. And it does look like a.ravel('F') is the same as a.T.ravel(). Hmmm. Now I wonder about this:
In [62]: array([[1,2,3],[4,5,6]], dtype=int8, order='F').flags
Out[62]:
CONTIGUOUS : False
FORTRAN : True
OWNDATA : True
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
Now, either CONTIGUOUS is in error, because it really *is* fortran contiguous (but not c contiguous), or the array cannot be passed to a fortran routine that expects fortran ordering, or CONTIGUOUS refers to C addressing, which we already know is not contiguous, in which case we feel uncertain. Note that knowing the answer matters if I want to call a fortran routine with this by pulling out the data pointer. The fortran routine could be in a library, or maybe in the LaPack wrapper, but whatever, it hasn't been wrapped by f2py that takes care of such details.
This also looks fishy:
In [93]: asfortranarray(array([[1,2,3],[4,5,6]], dtype=int8))
Out[93]:
array([[1, 2, 3],
[4, 5, 6]], dtype=int8)
In [96]: asfortranarray(array([[1,2,3],[4,5,6]], dtype=int8)).flags
Out[96]:
CONTIGUOUS : False
FORTRAN : True
OWNDATA : True
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
because the docstring says:
asfortranarray(a, dtype=None)
Return 'a' as an array laid out in Fortran-order in memory.
Which doesn't seem to be the case here. I am beginning to wonder if we really need fortran order, seems that a few well chosen interface routines would fill the need and avoid much confusion.
Chuck
On 17/10/06, Charles R Harris <[EMAIL PROTECTED]> wrote:
>
>
> On 10/17/06, Travis Oliphant <[EMAIL PROTECTED] > wrote:
> > Thus, reshape does the equivalent of a Fortran ravel to [1,4,2,5,3,6]
> > and then a Fortran-order based fill of an empty (3,2) array: giving you
> > the result.
>
> Why a Fortran ravel? I am thinking of it as preserving the memory layout,
> just messing with how it is addressed.
Because, to first order, the memory layout is totally irrelevant to a
python user.
array([[1,2,3],[4,5,6]],order='C')
array([[1,2,3],[4,5,6]],order='F')
should be nearly identical to the python user.
So what is the point of having a fortran layout if things are not actually layed out in fortran order? As far as I can see, memory layout is the only reason for fortran ordering. Now I can sort of see where the fortran ravel comes from, because the result can be passed to a fortran routine. And it does look like a.ravel('F') is the same as a.T.ravel(). Hmmm. Now I wonder about this:
In [62]: array([[1,2,3],[4,5,6]], dtype=int8, order='F').flags
Out[62]:
CONTIGUOUS : False
FORTRAN : True
OWNDATA : True
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
Now, either CONTIGUOUS is in error, because it really *is* fortran contiguous (but not c contiguous), or the array cannot be passed to a fortran routine that expects fortran ordering, or CONTIGUOUS refers to C addressing, which we already know is not contiguous, in which case we feel uncertain. Note that knowing the answer matters if I want to call a fortran routine with this by pulling out the data pointer. The fortran routine could be in a library, or maybe in the LaPack wrapper, but whatever, it hasn't been wrapped by f2py that takes care of such details.
This also looks fishy:
In [93]: asfortranarray(array([[1,2,3],[4,5,6]], dtype=int8))
Out[93]:
array([[1, 2, 3],
[4, 5, 6]], dtype=int8)
In [96]: asfortranarray(array([[1,2,3],[4,5,6]], dtype=int8)).flags
Out[96]:
CONTIGUOUS : False
FORTRAN : True
OWNDATA : True
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
because the docstring says:
asfortranarray(a, dtype=None)
Return 'a' as an array laid out in Fortran-order in memory.
Which doesn't seem to be the case here. I am beginning to wonder if we really need fortran order, seems that a few well chosen interface routines would fill the need and avoid much confusion.
Chuck
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