Bill Allombert on Tue, 18 Sep 2007 01:45:04 +0200 |
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Re: adding Proof option to factor() |
On Wed, Sep 12, 2007 at 12:35:03PM +0200, Karim Belabas wrote: > * John Cremona [2007-09-07 11:18]: > > The factor() function for integers (i.e. factorint()) does not provide > > factors which are proved to be prime, unless they are are < 10^15, > > accoriding to the manual. The manual recommends using isprime() in > > circumstances where proven primes are required. > > > > Could we add another flag to the function which defaults to 0 but if > > set does the proving step too? I use pari's factor() in mwrank and am > > not happy that I cannot guarantee results because of this, and it > > would be a lot easier to just add af lag to the call I make to > > factor(). > > I don't like complicating the user interface for something which is easy to > implement externally, usually in a more flexible way. There's already an > optional argument to factor, and having two flags is very error-prone > [ consider factor(n,1), factor(n,,1), factor(n,100000,1), > factor(n,1,10000), etc. ] Please note that we have factorint which already accept a flag. But actually what we need is a default(), not a flag: factorisation is a pervasive operation in PARI/GP, and if you want a proven result, you have to prove each and every factorizations that occurs during the computation. That would be something like: ? default(factor_proven,1) This is the reason factor_add_primes is a default and not a flag. Cheers, Bill.