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From: Dave Steffen (steffend_at_[hidden])
Date: 2001-03-12 20:57:38

David Abrahams writes:
> From: <walter_at_[hidden]>
> > > _ dense and sparse matrices
> >
> > Sparse matrices seem somewhat controversial to me. BLAS for
> > example handles only certain types of dense matrices like
> > general, symmetric, banded etc. BLAS does not support sparse
> > matrices.
> For the work I will be doing, sparse matrices are an absolute
> neccessity.

 Me too. The difficulty there seems to be that there's more than one
 way of implementing a sparse matrix, and which way you choose depends
 on how you're going to use it. By which I mean that if you're going
 to write into it once and then read sequentially a million times, you
 want to implement your sparse matrix one way; if you're going to
 continually access, change, and remove elements, you're going to
 implement it in another. This is why I like TNT's approach, where
 sparse matrices are implemented as sparse vectors of sparse vectors,
 and sparse vectors are templated on the underlying storage mechanism.

> Isn't BLAS, like, centuries old or something (spoken in valley-boy
> ingenue voice)? See also

 Yep, but it works, and is standardized. Duplicating BLAS'
 functionality in C++ is what Roldan Pozo's TNT project was about
 (although progress on that project seems to have stopped).

 That sparse BLAS project is a C project that just screams C++ at
 me. The idea (IIRC) is that they support a jillion different sparse
 matrix storage schemes, which means that each computational routine
 has different versions for each scheme or combination of schemes.
 The number of actual routines (each with unique names) therefore
 grows combinatorically. They have some kind of fancy automatic code
 generator that (effectively) duplicates C++'s template facility, and
 actually pumps out all the different routines; I seem to recall that
 the whole shebang was at around 80K LOC and isn't done yet.

 Of course, we could just use templates and have the compiler do all
 that work. This seems pretty obvious to me; given that Roldan Pozo
 is invovled in the sparse BLAS project, and I know he knows C++, I'm
 at a loss to know why they didn't use C++ for the project to begin with.

 OTOH, maybe that's a big, red, flashing neon sign telling Boost to
 get busy? ;-) ;-)

Dave Steffen Wave after wave will flow with the tide
Dept. of Physics And bury the world as it does
Colorado State University Tide after tide will flow and recede
steffend_at_[hidden] Leaving life to go on as it was...
                                                        - Peart / RUSH
"The reason that our people suffer in this way....
is that our ancestors failed to rule wisely". -General Choi, Hong Hi

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