Charles Greathouse on Fri, 20 Feb 2015 06:18:59 +0100 |
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Re: moebius function |
Hi,I am doing tests on the moebius.It went well for a few days until tonight when It gave an error.A printscreen is attached.What is the problem?Is the m on the screen reliable?By the way: when I want to make a list. how do I send my output to a file in pari/gp?Thanks for your answer,Chris
From: Karim Belabas <Karim.Belabas@math.u-bordeaux.fr>
To: Chris De Corte <chrisdecorte@yahoo.com>
Cc: pari-dev@pari.math.u-bordeaux.fr
Sent: Tuesday, February 17, 2015 8:42 AM
Subject: Re: moebius function
* Chris De Corte [2015-02-17 04:34]:
> Your moebius function seems to do calculations for very high
> figures.But your prime function seems to only go for low figures.
prime(n) uses a naive O~(n) algorithm (see ??prime), whereas moebius() calls
factor / factorint which use subexponential algorithms in exp O~(log n)^(1/2).
> Is your moebius then reliable?
It is to the extent factor() is: there is a remote possibility that a
composite > 2^64 is incorrectly considered as prime (??factor).
[No example is known at present]
Use
default(factor_proven, 1)
to get rid of this possibility (or set factor_proven = 1 in your gprc).
This will slow down a little the arithmetic kernel, but it may be
tolerable, or even negligible, in your application ( at worst
O(log n)^logloglog(n) extra cost when needing to factor the integer n )
In any case, moebius() will remain much faster than prime() :-)
Cheers,
K.B.
--
Karim Belabas, IMB (UMR 5251) Tel: (+33) (0)5 40 00 26 17
Universite de Bordeaux Fax: (+33) (0)5 40 00 69 50
351, cours de la Liberation http://www.math.u-bordeaux.fr/~kbelabas/
F-33405 Talence (France) http://pari.math.u-bordeaux.fr/ [PARI/GP]
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