Hello Nir,
while tiding up the code, I had a small look ahead for the symmetric case and the Incomplete Cholesky (IC) factorizations. There are many mathematical papers on that topic with many interesting ideas.
As there was no "standard library" like ITSOL which I can interface. I think we have to either implement an IC on our own or integrate some existing code into Octave.
For the latter case, after some research I got attention to this paper
http://doi.acm.org/10.1145/200979.200986. The Fortran routines seem to work with the provided examples and they use a column oriented sparse input scheme as Octave does (too good to be true). The only problem I see is the licence. It's for "academic purpose only". But there is some "Request permission" link to some Copyright Clearance Center, where I think one can ask the authors, if they published their code under a free software license again.
Do you agree on this or do you have other ideas to continue with IC?
Kai