In 2008, I had to solve some linear equations of the form `Ax=b`

,
where `A`

was a sparse matrix (usually a design matrix for B-splines).
I wrote up a library called `cl-sparsematrix`

in one afternoon, and
put it on the web.

This was **not** a sophisticated library. It did three very basic
things: it helped construct a sparse matrix using a hash-table, had a
function to pack that up in CSC format, and finally, a function to
call UMFpack via CFFI to solve the equation mentioned above. This was
it. It worked fine for what I wanted to use it, but it was not a
sophisticated sparse matrix library.

I didn't have a need for sparse matrices ever since, and the library
succumbed to bit rot: some other libraries it depended on moved on,
quite substantially in some cases, and now it doesn't even load
cleanly. But I still get a few e-mails every month asking about this
library. So apparently there is a need in the CL community for a
sparse matrix library. I have no time to clean it up at the moment,
and you are probably better off writing your own. **The library is no longer available online**, because it doesn't work and I don't want to mislead people who are looking for a sparse matrix library.

When LLA is finalized, I will include sparse matrix functionality at some point. But LLA is undergoing (yet another) major reorganization now — I think I finally figured out how to interface native Lisp arrays to LAPACK in the implementations that support pinned arrays. So sparse matrices are not on the immediate horizon. Unless, of course, I need to solve sparse systems again, and hack up yet another quick-and-dirty solution.