Re: Is my understanding on how my 0-based vector access works correct?

[hermann@stamm-wilbrandt.de]

On 2026-09-16 12:07, Bill Allombert wrote:
> Yes, but you could also do
>   my(cf=contfrac(sqrt(d)), a=i->cf[i+1]);
> (this way cf is part of the context of the closure a)
Thanks, that is definitely better and I changed to it. Also the find
function now is named ..._m1() and returns 0-based positions for use 
with a(i):
https://github.com/Hermann-SW/uni-heidelberg/blob/main/scripts/pell.gp

> In you code, you are computing contfrac(sqrt(d)) using floating point.
> ? contfrac(sqrt(23))
> %5 = 
> [4,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,8,1,3,1,9]
> With 2.18.1, you can compute it exactly:
> ? contfrac(quadgen(4*23))
> %8 = [[4],[1,3,1,8]]
> which means it is 4 followed by 1,3,1,8 repeating infinitely.
That is great, not for code for oeis.org or a repo because
it will not work for backlevel versions of gp for others.

But really impressive for my work, succeeds where previous approach just 
fails!

hermann@8840hs:~/pari-2.18.1.alpha$ ./gp -q
? contfrac(sqrt(nextprime(10^5)))
[316, 4, 3, 3, 10, 1, 3, 1, 5, 2, 2, 9, 30, 90, 3, 7, 2, 1, 1, 1, 2, 32, 
1, 9, 1, 2, 1, 210]
? contfrac(quadgen(4*nextprime(10^5)))
[[316], [4, 3, 3, 10, 1, 3, 1, 5, 2, 2, 9, 30, 90, 3, 7, 2, 1, 1, 1, 2, 
32, 1, 9,
1, 2, 1, 210, 12, 1, 9, 3, 1, 1, 2, 18, 4, 1, 2, 2, 1, 9, 2, 1, 29, 2, 
3, 1, 1,
1, 3, 1, 5, 2, 10, 1, 1, 1, 2, 1, 10, 1, 69, 2, 1, 3, 1, 1, 1, 2, 1, 3, 
6, 2,
5, 1, 2, 1, 4, 3, 1, 1, 2, 1, 3, 1, 1, 9, 2, 11, 1, 12, 1, 1, 6, 3, 1, 
1, 5, 34,
1, 22, 2, 4, 1, 4, 1, 2, 1, 2, 2, 1, 1, 4, 1, 1, 4, 14, 1, 5, 4, 1, 5, 
1, 2, 2,
36, 1, 3, 1, 1, 19, 1, 5, 1, 1, 104, 1, 6, 1, 4, 2, 16, 5, 3, 1, 14, 1, 
1, 1, 44,
1, 1, 14, 1, 1, 4, 4, 1, 11, 1, 1, 2, 5, 6, 1, 1, 1, 1, 1, 1, 315, 1, 1, 
1, 1,
1, 1, 6, 5, 2, 1, 1, 11, 1, 4, 4, 1, 1, 14, 1, 1, 44, 1, 1, 1, 14, 1, 3, 
5, 16,
2, 4, 1, 6, 1, 104, 1, 1, 5, 1, 19, 1, 1, 3, 1, 36, 2, 2, 1, 5, 1, 4, 5, 
1, 14,
4, 1, 1, 4, 1, 1, 2, 2, 1, 2, 1, 4, 1, 4, 2, 22, 1, 34, 5, 1, 1, 3, 6, 
1, 1, 12,
1, 11, 2, 9, 1, 1, 3, 1, 2, 1, 1, 3, 4, 1, 2, 1, 5, 2, 6, 3, 1, 2, 1, 1, 
1, 3,
1, 2, 69, 1, 10, 1, 2, 1, 1, 1, 10, 2, 5, 1, 3, 1, 1, 1, 3, 2, 29, 1, 2, 
9, 1,
2, 2, 1, 4, 18, 2, 1, 1, 3, 9, 1, 12, 210, 1, 2, 1, 9, 1, 32, 2, 1, 1, 
1, 2, 7,
3, 90, 30, 9, 2, 2, 5, 1, 3, 1, 10, 3, 3, 4, 632]]
?

Regards,

Hermann.