Thilina,

On Wed, Jul 3, 2013 at 8:00 AM, Thilina Rathnayake
<[email protected]> wrote:
>
>
>
> Hi Ondrej,
>
> I don't know much about solving recurrence relations on two variables, but
> the sources
> I am referencing provides the solutions for the recurrences involved with
> Pell equation.
> So, I think that would be enough.

Absolutely.

>
> Concerning the solutions of x**2 - 13*y**2 = 27, solutions returned by
> diop_pell
> are:
>>>> diop_pell(13, 27)
> [(220, 61), (40, 11), (768, 213), (12, 3)]
>
> Here is how wolfram alpha represents it:
> http://www.wolframalpha.com/input/?i=x**2+-+13*y^2+%3D+27
>
> They provide general solutions for each class.
> (Look in the box named "Integer solutions")

It has 4 solutions, the first one is:

x = ±1/2 (-40 (649-180 sqrt(13))^n+11 sqrt(13) (649-180 sqrt(13))^n-40
(649+180 sqrt(13))^n-11 sqrt(13) (649+180 sqrt(13))^n),   y = ±1/26
(-143 (649-180 sqrt(13))^n+40 sqrt(13) (649-180 sqrt(13))^n-143
(649+180 sqrt(13))^n-40 sqrt(13) (649+180 sqrt(13))^n),   n element Z,
n>=0

How is this solution mapped to one of the numbers in [(220, 61), (40,
11), (768, 213), (12, 3)] ?

Ondrej

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