Hello Gilles, > [...] > >> I fully agree. We could also opt for a less correct, but more >> efficient solution: we do not store the sign of zero, and return NaN >> each time v / zero occurs. The result should be NaN anyway, because >> its sign is undecidable. This specificity would be clearly stated in >> the javadoc. What do you think? > > We had this sort of discussion with the "Complex" class, where there are > such issues as "standard" vs "correct" vs "documented" etc. E.g. some > computations return "NaN" where it should be "infinity" (or vice-versa, I > don't remember exactly). See MATH-667: > https://issues.apache.org/jira/browse/MATH-667 > > Maybe that we must be guided with some use-cases for this class. > Maybe in actual uses, the problems discussed here do not appear, and any > additional check would destroy the usefulness of this class in such cases > (just a wild guess). Maybe that we should drop support for sparse vectors! > I fully agree with you. Speaking quite honestly as a user of the linear package, even if I know that IEEE floats handle infinite values well, I tend to dish results that contain those values, and try to cure the cause of these unwanted values. So, as a user, whether the method returns NaN of infinity does not matter to me (as long as it does not return zero --or any normal value-- quietly): in any case, I would do a computation again, this time with "correct" values.
I also think that in this case, strict adherence to IEEE standards (which were written for scalar values, not vectors) should not compromise the performance of the class. I would be more cautious with your suggestion about getting rid of sparse vectors. I think it's nice to have them, even if the support is limited (we should of course concentrate on array-based vectors first). As long as we clearly document these limits, I'd like to keep them. Besides, with the new set of abstract tests being constructed for any vector class, it should be possible in the future to propose and test a better implementation. The problem we have is clearly lack of feedback on these features (remember the debates we had on the "sparseIterators"-- not perfect, but experience only can tell how to improve). Best regards, Sébastien --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
