Re: Sparse matrices?

[Ian Searle]

Stef Pillaert BK wrote:
> 
> Hello,
> 
> I'm wondering... is it possible in octave to work with sparse matrices to
> save some space? (if not, is there a chance that it will be in the near
> future?)
> 
> Thanks.
> 
> Stef address@hidden

Having just added sparse matrices to RLaB (no plug intended). I can
offer some information. It is far more difficult and time consuming than
it looks! Seemingly trivial operations like:

  a[i;j] = x;

are difficult to implement... not to mention an efficient
implementation. 

I choose compressed row-wise sparse storage. With the aid of hindsight,
I might have choosed compressed column-wise sparse storage.

Then, once sparse structures and operations are implemented comes the
joy of finding an efficient, and free sparse non-symmetric solver, and
graph partitioning/re-ordering packages.

All in all, a considerable amount of work. I was very fortunate that
some users (one in particular) have very good educations in linear
algebra.

Cheers,
-- 
Ian Searle
address@hidden