Diagonal v. sparse matrices [was Re: deprecated functions]

[Jaroslav Hajek]

On Wed, Mar 4, 2009 at 10:17 PM, John W. Eaton <jwe at octave.org> wrote:
> On  4-Mar-2009, Jaroslav Hajek wrote:
>
> | Nope, I didn't break compatibility that much :) This is, in fact, the
> | standard Matlab way to create a sparse diagonal matrix. It would be
> | nice, however, to be able to write this as sparse(diag()) as well
> | without losing efficiency. It seems Jason is working on something
> | along that lines, so I'd leave it to him. Note that the proper
> | constructors are already defined in liboctave.
>
> What do you mean by "without losing efficiency"?  Does
>
>  a = diag (...);
>  sparse (a);
>
> convert A to full first, then sparse?

... yes.

> If so, it seems that should be fairly easy to fix.

It was really quite straightforward - fix is online. It also uncovered
the fact that the diag -> sparse constructors were broken, so
everything should be OK now. sparse() now works efficiently on
diagonal and permutation matrices.

> In any case, I think the following change should
> be made to spdiag.  This is much simpler than having to check
> arguments in spdiag, and will be efficient if the "sparse (diag)"
> constructor is fixed.  But the important thing is that for
> compatibility with previous versions of Octave, spdiag returns a
> sparse matrix, not a diag matrix.  Do you agree?

Agreed.

> diff --git a/scripts/deprecated/spdiag.m b/scripts/deprecated/spdiag.m
> --- a/scripts/deprecated/spdiag.m
> +++ b/scripts/deprecated/spdiag.m
> @@ -28,9 +28,9 @@
>   if (! warned)
>     warned = true;
>     warning ("Octave:deprecated-function",
> -            "spdiag is obsolete and will be removed from a future version of Octave; please use diag instead");
> +            "spdiag is obsolete and will be removed from a future version of Octave; please use sparse (diag (...)) instead");
>   endif
>
> -  retval = diag (varargin{:});
> +  retval = sparse (diag (varargin{:}));
>
>  endfunction
>
>
> jwe
>
>



-- 
RNDr. Jaroslav Hajek
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz