Re: [Starpu-devel] [starpu_matrix_interface: nx, ny]

[Samuel Thibault <samuel.thibault@inria.fr>]

Hello,

Maxim Abalenkov, on mer. 13 déc. 2017 11:57:10 +0000, wrote:
> I have a very simple question. Can you please confirm what are the nx and 
> ny in
> the starpu_matrix_interface? Are they the no. of rows and columns of the
> matrix?

Yes.

> In this case where is the origin (0, 0) of the matrix?
> Is it in the top left corner? I couldn’t find this information in
> the Handbook.

StarPU does not actually care about which corner of the matrix this is.
For StarPU 0,0 is just the first element of the memory area.

You can for instance take the convention used by BLAS libraries, see
their documentation. Note also that there is a C vs Fortran convention,
explained in BLAS libraries documentations.

Also, note the notion of ld (leading dimension), which is important when
accessing a submatrix.

> I’m looking at the example of multiple views in the source file
> “fmultiple_manual.c”. Line 139 of the code registers the
> “vertical slices” of size NX, NX/PARTS, NY.

Yes, the matrix is here split in PARTS pieces of NX/PARTS times NY
elements, thus vertical slices.

> "Horizontal slices" are registered with size NX, NX, NY/PARTS.

And there the matrix is split in PARTS pieces of NX times NY/PARTS
elements, thus horizontal slices.

Samuel