On Thu, Dec 18, 2025 at 12:52 PM Dima Pasechnik <[email protected]> wrote: > > Maxim Kontsevich reported patently wrong answers from modular forms > code in https://github.com/sagemath/sage/issues/41267. > We were able to pin them down to setting Parallelism().set(nproc=k), > for any k>1. The error is not dependent upon the platform (observed > in Linux Conda originally, but meanwhile found to occur in "normal" > builds, too, on Linux x86_64 and on Intel macOS) - arm64 etc still > needs to be checked. > > It would be great to understand what fixed it - any ideas?
(Pure speculation below, but I did write CuspForms so maybe it's helpful.) Just looking at your log: sage: Parallelism() Number of processes for parallelization: - linbox computations: 1 - tensor computations: 1 sage: CuspForms(Gamma1(2), 10).hecke_matrix(5) [870] sage: Parallelism().set(nproc=2) sage: Parallelism() Number of processes for parallelization: - linbox computations: 2 - tensor computations: 2 sage: CuspForms(Gamma1(2), 10).hecke_matrix(5) [534154/3] and seeing "linbox" makes me thing "maybe there is a bug in linbox"? I don't even know what "Parallelism()" is, but my guess is it sets a parameter that impacts how linbox runs. Modular forms computations use linbox for fast exact linear algebra, and maybe there's a bug in linbox. Linbox is very actively developed so maybe a routine upgrade fixed that bug. > > For reasons unclear to me, the git history between tags 10.6 and 10.7 > is not clean (somehow, 10.7 is not "based" upon 10.6 in Git sense), > breaking a straightforward git bisect. > Help with the latter would be appreciated, too. > (otherwise one would need to do a manual git rebase of 10.7 over 10.6, > which isn't instant) > > Dima > > PS. Computations done in Sage 9.7-10.6 under Parallelism().set(nproc=k) > (e.g. one might have set "Parallelism().set(nproc=42)" in ~/.sage/init.sage/) > thus might be incorrect :-( > > -- > You received this message because you are subscribed to the Google Groups > "sage-release" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/sage-release/CAAWYfq0NoeR%2BxKRsKgvk-0P5PHyk1Tnc35gXhxXs-rSwc6gM-g%40mail.gmail.com. -- William (http://wstein.org) -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/sage-devel/CACLE5GB%2BL%2BjQYgjM-RpyhWMFTuX4Ty9A8qKvZ8jdx8J4Vg9n-g%40mail.gmail.com.
