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John Cremona on Sat, 09 Jan 2016 18:13:26 +0100
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Re: Re[2]: fibonacci(n) for large n's
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- To: Zak Seidov <zakseidov@yahoo.com>
- Subject: Re: Re[2]: fibonacci(n) for large n's
- From: John Cremona <john.cremona@gmail.com>
- Date: Sat, 9 Jan 2016 17:12:49 +0000
- Cc: Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>, "pari-users@pari.math.u-bordeaux.fr" <pari-users@pari.math.u-bordeaux.fr>
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On 9 January 2016 at 17:04, Zak Seidov <zakseidov@yahoo.com> wrote:
> Great,
> Bill's code is much more faster than standard fibonacci(n).
> Then my Q is:
> why not to implement this code in PARI's fibonacci(n)?
> One related however silly Q:
> How to retrieve 5 in result of, say, Mod(12,7)?
> PARI gives as a result Mod(5,7) but how to retrieve 5?
lift()
e.g. lift(Mod(5,7)) --> 5
Johhn
> (sorry my math and PARI level is so low:()
> Thx,Zak
>
>
> Пятница, 8 января 2016, 19:35 +01:00 от Bill Allombert
> <Bill.Allombert@math.u-bordeaux.fr>:
>
> One simpler and faster way is
> myfibo(n)=polcoeff(lift(Mod(x,x^2-x-1)^n),1)
>
> which you can restrict mod m:
> myfibomod(n,m)=polcoeff(lift(Mod(x*Mod(1,m),x^2-x-1)^n),1)
>
> Cheers,
> Billl.
>
>