On Tue, Jun 10, 2014 at 09:22:26PM +0200, Julien Puydt wrote: > Hi, > > Le 10/06/2014 21:09, Bill Allombert a écrit : > >On Tue, Jun 10, 2014 at 04:19:11PM +0200, Julien Puydt wrote: > >>Hi, > >> > >>Le 10/06/2014 15:14, Bill Allombert a écrit : > >>>On Tue, Jun 10, 2014 at 07:13:03AM +0200, Julien Puydt wrote: > >>>>Hi, > >>>> > >>>>Peter Bruin bissected the problem down to a commit (8cfb9c6b, > >>>>incorrect rounding in mulur), see comment #91 on the sage bug. > >>> > >>>First, I need to clarify that PARI never promised to return identical > >>>results > >>>on 32 and 64 bit platforms, and I do not see anything wrong with commit > >>>8cfb9c6b. > >>> > >>>Secondly, on the face of it, the issue is catastrophic cancellation in > >>>computel.gp, in the loop > >>>for(y=1,ncoeff,Gvec[d+y]=1.*sum(j=1,d,subst(recG[j],n,y)*Gvec[d+y-j])); > >> > >>Well, since such cancellation wasn't an issue before, that stops the > >>sage people from transitioning out of a heavily patched pari to the > >>latest upstream. > > > >As far as I know, the cancellation was an issue before, just not in this > >particular example. > > I find the fact that it was working on 32bits with pari 2.5 and it's > now failing on 32bits with pari 2.7 disturbing...
I found out that upstream patch 6b271ef31 leads to the same lucky behaviour on 2.7 than on 2.5. This patch will be included in PARI 2.7.2 (git commit 08d35a5b) Cheers, -- Bill. <[email protected]> Imagine a large red swirl here. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
