GSoC with Flint - Week 1105 Aug 2014
This week I've worked on a variety of different things, unfortunately getting hung up on most of them!
First I found some bugs in my Saunders-Wan Smith normal form code, most of them ended up being fixable, however one still eludes me. It seems the bug is fairly rare (occurs for roughly 1 in 10000 test cases) and it is certainly related to the random nature of the algorithm but my current thinking is that the current behaviour should not be happening even when we get unlucky with the randomness. I've left this issue alone for now after spending a couple of days making no progress on it.
I then moved on to writing some general HNF/SNF methods that pick between available implementations based on matrix size, norm and anything else that I could work out as being relevant. While doing this I found that the Kannan-Bachem Hermite form method worked better than the modular method some of the time and so I decided to try and combine them into a modular method that works by taking minors into HNF rather than rows. I had some problems making this work correctly when the input was not of full rank and all the fixes I tried ended up having some corner case that made them fail. It just occurred to me however that when the modular method is used as part of the Pernet-Stein algorithm the matrix given is always square and so this was not perhaps a completely wasted effort.
I then moved back to working on Pernet-Stein, specifically I added capacity for non-full row rank matrices, and fully general matrices should be done very soon.
This week I'm going to be doing some profiling and comparisons between my implementations and existing ones and try and work out the reasons why certain results are as they are and how the HNF/SNF methods I now have can be made faster in the future. It should be helpful to have a note of the barriers to having faster HNF/SNF computation in Flint and how they could be overcome.
Of course I'll also be tidying up and documenting several bits as I go along to fill in any gaps in functionality I have left along the way.