[SciPy-user] Sparse v. dense matrix, SVD and LSI-like analysis

[Nick Arnett]

Robert Kern wrote:

> An SVD is not the same as an eigen decomposition.
> 
> http://mathworld.wolfram.com/EigenDecomposition.html
> http://mathworld.wolfram.com/SingularValueDecomposition.html

That dawned on me not too long after posting.  Fuzzy brain this week, a 
birth and a death in the family a few days apart.

> In any case, all of the linalg.* functions only operate on dense arrays, 
> not sparse matrices.

Ummm, now I'm thinking I'm in over my head.  SVD is a matrix operation 
isn't it?  I was imagining that an array of mostly zeros would be the 
equivalent of a sparse matrix, so that SVD would apply to it for what 
I'm doing, which is related to latent semantic analysis.

Am I way off-base here?  My understanding of Scipy isn't great, 
compounded by a less-than-great grasp of the mathematics.  Learning as 
go, in large part.

Any help gratefully accepted.

Nick