Thank you for yor clear explanation. Julián Aguirre
On 16 mar, 18:23, John Cremona <john.crem...@gmail.com> wrote: > Let me explain (as the author of mwrank). There was a bug in > mwrank, found by James Wiegandt and Edray Goins, which meant that in > some cases for curves with rational 2-torsion the computed upper bound > on the rank was too high. (Technical explanation: the second descent > homogensous spaces were not being checked for solvability of the > reals, so when there was such a space which is soluble over all Q_p > but not over the reals it was wrongly being counted as an element of > the Selmer group.) > > At the same time as fixing that, I improved some of the output > messages, and enhanced the interface fo ease of use by Sage. > > This is documented (briefly) athttp://trac.sagemath.org/sage_trac/ticket/8184 > showing that the fix has been in Sage since 4.3.3 (and maybe in the > mwrank source code also). > > John Cremona > > On Mar 16, 1:48 pm, Julian <julian.agui...@ehu.es> wrote: > > > Dear group, > > > I have noticed a change in behaviour of mwrank when called from SAGE > > 4.3.3 to compute Selmer ranks. I am using Mac OSX 10.6.2, Power PC. > > The SAGE folder is in the directory Applications. The command > > > u003429:~ julianaguirre$ /Applications/sage/sage -mwrank -v0 -s > > > gives > > > Program mwrank: uses 2-descent (via 2-isogeny if possible) to > > determine the rank of an elliptic curve E over Q, and list a set of > > points which generate E(Q) modulo 2E(Q). and finally saturate to > > obtain generating points on the curve. For more details see the file > > mwrank.doc. For details of algorithms see the author's book. > > > Please acknowledge use of this program in published work, and send > > problems to john.crem...@gmail.com. > > > Version compiled on Feb 21 2010 at 22:52:52 by GCC 4.0.1 (Apple Inc. > > build 5490) > > using base arithmetic option NTL_ALL (NTL bigints and multiprecision > > floating point) > > > Enter curve: [0,92390679642986,0,378762423029040806906245225,0] > > > >Curve [0,92390679642986,0,378762423029040806906245225,0] : selmer-rank = 9 > > >upper bound on rank = 7 > > > In the previous version the output was > > > >Curve [0,92390679642986,0,378762423029040806906245225,0] : selmer-rank = 7 > > > Any idea of what is going on? > > > Julian -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
