#1305 - gp core() function: could do better?

PARI/GP Bug report logs - #1305
gp core() function: could do better?

Reported by: Kevin Buzzard <k.buzzard@imperial.ac.uk>

Date: Mon, 19 Mar 2012 11:18:16 UTC

Severity: normal

Done: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>

Bug is archived. No further changes may be made.

Message #10 received at 1305@pari.math.u-bordeaux.fr (full text, mbox, reply):

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From Karim.Belabas@math.u-bordeaux1.fr Mon Mar 19 13:17:22 2012
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Date: Mon, 19 Mar 2012 13:17:16 +0100
From: Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr>
To: Kevin Buzzard <k.buzzard@imperial.ac.uk>, 1305@pari.math.u-bordeaux.fr
Subject: Re: Bug#1305: gp core() function: could do better?
Message-ID: <20120319121716.GA18235@math.u-bordeaux1.fr>
References: <Pine.LNX.4.64.1203191057430.22497@crackerjack.ma.ic.ac.uk>
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Hi Kevin, * Kevin Buzzard [2012-03-19 12:37]: > [Sorry -- I should upgrade to 2.5.1, but I didn't yet, and I don't > see core mentioned in the changelog 2.5.0->2.5.1 so let me gamble > that this is still an issue] > > What do you think of this? No good :-) > (11:00) gp > isprime(10^1000+1) > %1 = 0 > (11:00) gp > core(5*(10^1000+1)^2) > [gp now goes into a very long loop, presumably because it's trying > to factor (10^1000+1)^2?] Trying to factor 10^1000 + 1, rather. > I am not C++-savvy enough to know what the "core" function was doing > in 2.5.0, but in this particular case I can see a relatively simple > way of spotting the answer: if we use trial division or ECM or > whatever to find a few small factors, then could it be worth > checking to see if what we have left is a square?? If it is then > we're done. Presumably core() is not currently doing this... Currently core(n) is implemented via F = factor(n); weed_out_stuff_from(F); which is suboptimal for your example, even if factor() is trying to be clever. I'll try to come up with a nice generic implementation (as opposed to a quick hack starting from a full copy of the factoring engine + minor tweakings to hunt for square factors). 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/~belabas/ F-33405 Talence (France) http://pari.math.u-bordeaux1.fr/ [PARI/GP] `

Bill Allombert <allomber@math.u-bordeaux.fr>. Last modified: Sat Aug 26 17:05:00 2023; Machine Name: pari

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PARI/GP Bug report logs - #1305 gp core() function: could do better?

PARI/GP Bug report logs - #1305
gp core() function: could do better?