[Gsll-devel] Extracting sub-matrices and sub-vectors?

[Liam Healy]

Malcolm,

Try #'column, #'row.  They are also setfable.  These will give you
individual columns and rows from a matrix, as a vector (mvector).
As for general submatrix or subvector,
the answer is no.  There actually are functions in GSL that will
provide matrix "views"
http://www.gnu.org/software/gsl/manual/html_node/Matrix-views.html
but I haven't implemented them yet because of uncertainty of their
value and the complexity of getting it right.  There was a discussion
on this list earlier about how/whether to do this; I think Tamas had
some nice ideas but again, I've not implemented them at this point.

Liam

On Wed, Apr 29, 2009 at 2:16 PM, Malcolm Reynolds
<malcolm.reynolds at gmail.com> wrote:
> Hi guys,
>
> I've been out of the country for a while but I'm getting back to work
> on my project. Something else I've been wondering about for GSLL is
> whether there is a way to quickly extract sub-matrices and especially
> sub-vectors from a matrix. Something with power equivalent to the
> matlab indexing using a colon to express ranges would be amazing but I
> guess probably quite nasty to implement efficiently. However, what
> would help me even more right now is a way to extract rows / columns
> from a matrix, without copying. I currently use a do-loop to run
> through the indices I want, but since the internals of the storage
> appear to be row major, is there a way to get a "pointer" (not sure if
> this is preferred lisp terminology, sorry) to an individual row?
>
> To clarify, if I do
>
> (defvar x (make-marray 'double-float :initial-contents '((1 2 3) (4 5
> 6) (7 8 9))))
>
> is there any efficient way (ie don't need to copy element by element
> to a new object) thatI can get a reference to the row (4 5 6) of that,
> either as a gsll::matrix or gsll::vector object? If structure was
> shared between the matrix and the vector that would be no problem, it
> would be ideal in fact.
>
> Regards
>
> Malcolm
>
> Malcolm
>