PARI/GP Bug report logs - #1151
rnfequation(,,1) is broken

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X-Loop: allomber@math.u-bordeaux.fr
From: allomber@math.u-bordeaux.fr (PARI/GP Bug Tracking System)
To: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>
Cc: Karim.Belabas@math.u-bordeaux.fr
Subject: Bug#1151: marked as done (rnfequation(,,1) is broken)
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In-Reply-To: <20110208204736.GA18741@math.u-bordeaux1.fr>
References: <20110208204736.GA18741@math.u-bordeaux1.fr> <20101218155503.GC9570@yellowpig>
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Your message dated Tue, 8 Feb 2011 21:47:36 +0100
with message-id <20110208204736.GA18741@math.u-bordeaux1.fr>
and subject line Bug#1151: rnfequation(,,1) is broken
has caused the attached Bug report to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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Bill Allombert
(administrator, PARI/GP bugs database)

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Date: Sat, 18 Dec 2010 16:55:03 +0100
From: Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>
To: submit@pari.math.u-bordeaux.fr
Subject: rnfequation(,,1) is broken
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Package: pari
Version: 2.4.3, 2.3.5

Hello Karim,
This issue was reported on the pari-users list
<http://pari.math.u-bordeaux.fr/archives/pari-users-1012/msg00004.html>.
I report it for reference.

? f = (y^17-1)/(y-1);
? g = Mod(1,f)*x+Mod(y^6,f);
? rnfequation(f,g,1);
  ***   at top-level: rnfequation(f,g,1)
  ***                 ^------------------
  *** rnfequation: the PARI stack overflows !

Cheers,
Bill

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Date: Tue, 8 Feb 2011 21:47:36 +0100
From: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>
To: Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>,
	1151-close@pari.math.u-bordeaux.fr
Subject: Re: Bug#1151: rnfequation(,,1) is broken
Message-ID: <20110208204736.GA18741@math.u-bordeaux1.fr>
References: <20101218155503.GC9570@yellowpig>
 <20110131235925.GE3266@yellowpig>
 <20110201162149.GF3266@yellowpig>
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* Bill Allombert [2011-02-01 17:57]:
> On Tue, Feb 01, 2011 at 12:59:25AM +0100, Bill Allombert wrote:
> > On Sat, Dec 18, 2010 at 04:55:03PM +0100, Bill Allombert wrote:
> > > Package: pari
> > > Version: 2.4.3, 2.3.5
> > > 
> > > Hello Karim,
> > > This issue was reported on the pari-users list
> > > <http://pari.math.u-bordeaux.fr/archives/pari-users-1012/msg00004.html>.
> > > I report it for reference.
> > > 
> > > ? f = (y^17-1)/(y-1);
> > > ? g = Mod(1,f)*x+Mod(y^6,f);
> > > ? rnfequation(f,g,1);
> > >   ***   at top-level: rnfequation(f,g,1)
> > >   ***                 ^------------------
> > >   *** rnfequation: the PARI stack overflows !
> > 
> > Well, according to my calculation the correct LERS is:
> > (-x^4 + x^3 - x^2)*y + (-x^7 + x^6 - x^5)
> > 
> > Furthermore, the values returned by Flx_resultant_all for x=2 are 144 times too large.
> > For x=3 the values are random but the quotient H0/H1 seems correct
> 
> The attached patch is probably incorrect, but it allows both 'make test-all' and 
> this test
> for(i=1,16,print(i);rnfequation(polcyclo(17,y),-x+y^i,1))
> 
> to work. Strange...

Fixed in svn, using quite different formulas (cf Algorithm 3.3.7 in GTM138).

Thanks !

    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/~belabas/
F-33405 Talence (France)       http://pari.math.u-bordeaux1.fr/  [PARI/GP]
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