On Sat, Apr 12, 2008 at 12:18:11PM -0400, Liam Healy wrote:
Currently, the affine maps are not in FFA, but it appears that views in GSL need them. If you need affine maps, let me know, I can whip up something on top of the current FFA (so even with these very general arrays, one could always access the underlying Lisp array if needed, I consider that an advantage).
For the type of affine map that GSL views support, would it be straightforward to support those views through FFA? If so, go ahead and whip it up.
It would be straightforward to support them with a _layer_ over FFA, but not inside FFA (because they would no longer be Lisp arrays). To be honest, I don't really need views right now, and I have other higher-priority things I am working on, so I am not interested in writing something quick and dirty at the moment.
Right, this was my motivation for skipping over them in the first place. As I said before, I didn't even bother to figure out if they would work. They just seemed unimportant. I think native arrays via SBCL are more important, so that's what I've been focusing on (to the extent that I've had time to work on GSLL).
I agree with your original evaluation - views are not that important, a pain in the ass to integrate, so we should be focusing on other stuff first. I would not mind ignoring views altogether (ie simply not implementing those functions that need views) for the short or medium run. But I am probably biased. I am using GSLL for the functions/algorithms which are a pain in the ass to implement and debug in any language, so I just want to use versions somebody else wrote. For example, special functions like erf of the gamma function, splines, multivariate optimization, etc. I think views are used because of optimization, to avoid copying. My experience is that copying is fast and is generally not a hot spot in the programs I write. So I am not interested in implementing something that would lead to a 0.1% speed improvement in my programs, but would entail the loss of the ability to use native Lisp arrays seamlessly and also a huge amount of unnecessary debugging and scaffolding code. I also understand that other users may need views in GSLL. But before embarking on a project to integrate them, I would like to see some real-world application where the profiling says that views would save a lot (at least 10%) of runtime, and it is not possible to do it by other means (reorganizing data structures, displaced arrays, etc). Tamas