Karim Belabas on Fri, 03 May 2013 20:07:53 +0200 |
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Re: Problems with elldivpol - will they be fixed in 2.6.0? |
* Richard in Reading [2013-05-03 18:58]: > I obtained pari-2.6.0.svn13433.tar,gz from the website and built it in an attempt to escape apparently incorrect elldivpol results which plagued previous pari versions for unix. > By contrast I have a version [2.5.1] running on Windows which apparently doesn't suffer from the same problem in this instance. > > So on the [2,6,0,"svn-13433"] version, if I do > > x=0;factor(eval(elldivpol(ellinit([0,-1,1,-10,-20]),13))) > x=0;factor(eval(elldivpol(ellinit([0,-1,1,-10,-20]),13))) > > it prints the factors 2731,185693,57084047 etc... > however if I then do > > e=ellinit(Mod([0,-1,1,-10,-20],2731));lift(ellpow(e,[0,ellordinate(e,0)[1]],13)) > > it prints [1360,2238] which I believe to indicate that 2731 is incorrect. Similar checks of the other factors fail. > > On the [2,5,1] version on Windows, two of the factors are > 27793 and 5141213801370234316849605048349 A few minor remarks: * I'd use polcoeff(T, 0) or subst(T,x,0), rather than x = 0; eval(T) to get the constant coefficient. * In 2.6, e = ellinit([0,-1,1,-10,-20], 2731) is the recommended way to define a curve over F_2731 Now on to your actual problem: I'm not too sure what [2,6,0,"svn-13433"] refers to yet (we dropped svn for git a long time ago, I don't know how to translate "SVN repository version 13433" to a git commit name at this point), but in any case it's a very old outdated version. In the up to date development branch for 2.6.0 (aka 'master'), version() outputs [2, 6, 0, "git-ca538f5"], and I correctly get (19:39) gp > x=0;factor(eval(elldivpol(ellinit([0,-1,1,-10,-20]),13))) %2 = [ 27793 1] [ 132199183 1] [ 3597411289 1] [5141213801370234316849605048349 1] > Does anyone have a good idea of the state of bugs in elldivpol for 2.6.0 ? No known bugs in the 'master' branch. You can check all currently open tickets in 2.6.0 from our Bug Tracking System at http://pari.math.u-bordeaux.fr/cgi-bin/pkgreport.cgi?pkg=pari (none of them concern elliptic curves) > I would be very grateful to receive instructions on how to build a version > that gives the correct results! You may either - install pari-2.5.3 from our Download page http://pari.math.u-bordeaux.fr/download.html - or give pari-2.6.0 a try (esp. for elliptic curve related work); the recommended way for this is to use 'git' http://pari.math.u-bordeaux1.fr/anongit.html (because bleeding edge versions may be very buggy and git simplifies updates) If for some reason, git doesn't work for you, a nighly snapshot is at http://pari.math.u-bordeaux1.fr/pub/pari/snapshots/ Feel free to report on further problems getting either versions to work. (I'm assuming a Linux machine above; for Windows, the Download page contains a recent snapshot that "should just work") Cheers, K.B. -- Karim Belabas, IMB (UMR 5251) Tel: (+33) (0)5 40 00 26 17 Universite Bordeaux 1 Fax: (+33) (0)5 40 00 69 50 351, cours de la Liberation http://www.math.u-bordeaux1.fr/~kbelabas/ F-33405 Talence (France) http://pari.math.u-bordeaux1.fr/ [PARI/GP] `