Re: [GSoC2014] Looking for a mentor

[Philip Nienhuis]

mfasi wrote
> Hi all,
> 
> I am a little bit sorry for spamming the maintainers list, but I was
> suggested to do so on IRC - and I am in good company. As the subject says,
> I am looking for a mentor to apply for the Google Summer of Code 2014. The
> topic I am interested in is the implementation of some matrix functions in
> Octave (project 
*
> Improve logm, sqrtm, funm
*
> ), as I already have a little experience on the domain. Further
> information on my 
> public application draft <http://wiki.octave.org/User:Mfasi>  
> . Thank you!

Have you found a mentor yet?
I regret I am too little proficient in linear algebra to help you out,
although I wrote the existing funm.m in the OF linear-algebra package. While
that works OK for my aims (relatively small (n < 100), well conditioned,
positive semi-definite symmetric matrices) I'd love to see a more robust
funm.m implementation. But be warned: as Higham wrote in his email to our
maintainers list, writing a robust funm.m from scratch is no easy task.

Just some remarks:

As to logm(), AFAIK that one has already been optimized by "Tommy Guy" some
years back, along the lines set out by Higham (IIRC Tommy Guy implemented
some of Higham's methods). I am not aware of things left out (maybe
complex?).

As you can see in the OF linear-algebra package, some matrix functions (trig
and hyperbolic) have been implemented, by invoking expm(), in the thfm.m
function in that same package. funm.m delegates those trig and hyperbolic
matrix functions to thfm.m. 
It would be wise to keep that structure intact.

Philip



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