But...
If you look at the dimension ordering in slicing
where dim(0) is the left-most index, then PDL is
actually using the same memory ordering as with
fortan: dim0 iterates first, then dim1 increases,
then dim2....
In fact sequence(3,4) is in memory in this
order: (0,0), (1,0), (2,0), (0,1), (1,1), (2,1),
(0,2), (1,2), (2,2), (0,3), (1,3), (2,3) which
is exactly the memory order of a(3,4) in fortran.
It seems the issue is that *displaying* the
data uses C ordering. If we were to display
the data as if transposed, then PDL would seem
to me to be a column major storage system.
I wonder what would happen if matrix operations
used the natural dimension order rather than
the imposed C ordering? It would get rid of
all the nasty transposes in the matrix multiplication
and things the tensor sums would compose naturally.
Am I the only one who thinks PDL for matrix ops is
a bit screwy---but for no good reason?
--Chris
On 6/4/2017 16:27, Grégory Vanuxem wrote:
Hi here,
https://docs.oracle.com/cd/E19957-01/805-4940/z400091044d0/index.html
Just for information.
Now, an other thing to know.
Imagine I have a 2x2 matrix.
If I write in the computer memory 4 integer’s (1-2-3-4) in one time,
in C this will be in matrix representation :
1 2
3 4
But in Fortran, like in mathematics :
1 3
2 4
So operations on these two representations are completely differents.
Generaly computations on matrices are done on a very low level and use
directly the memory areas (no aware of indexing scheme).
Hope that helps
__
Greg
*De : *Luis Mochan <mailto:[email protected]>
*Envoyé le :*jeudi 1 juin 2017 20:06
*À : *[email protected]
<mailto:[email protected]>
*Objet :*Re: [Pdl-general] SVD
Still confusing:
On Wed, May 31, 2017 at 03:36:33PM +1000, Karl Glazebrook wrote:
> column-major all the way down, as image processing came before
matrix ops and i in A(i,j) is naturally the x-axis.
but the x axis displays horizontally, as row, and when matrices are
multiplied i is interpreted as column index, i.e., as index along row.
> i.e. A[0,1] is followed by A[1,0] in memory
You mean A[0,0] is followed by A[1,0] in memory, right?
So memory is arranged as in fortran arrays (first index fastest), but
the interpretation as row and column indices is different.
Regards,
Luis
>
>
> Karl
>
>
>
> > On 22 May 2017, at 6:32 am, Chris Marshall
<[email protected]> wrote:
> >
> > Please ignore the following. Just mark me confused...
> >
> > --Chris
> >
> > On 5/21/2017 15:51, Chris Marshall wrote:
> >> The row-major and col-major for PDL has always
> >> confused me since, AFAICT the PDL dimensions and
> >> slicing syntax actually are column major in
> >> memory but we print them out in row-major.
> >>
> >> Maybe one of the original PDL developers could
> >> give an explanation (of the history at least!).
> >>
> >
> >
> >
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o
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