Pedro Patricio on Tue, 05 Nov 2019 16:19:46 +0100

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Re: Finding Y coordinate

So you want a modular square root?

? sqrt(Mod(2, 7))
%1 = Mod(3, 7)

I would firstly compute the Legendre symbol in order to check the square root exists...

Às 15:15 de 05/11/19, Tiago Mendes escreveu:
Good afternoon,

I am writing a file in C using the PARI C Library  and need some help. This is what i want to do:

- Given 

—— a prime p,  and

—— the coordinate X  

i want to obtain the value of Y coordinate from the curve Y^2 = X^3 + 7 (mod p) , knowing for example that Y is positive. 

os meus cumprimentos

Tiago Mendes

pedro patricio
departamento de matematica
universidade do minho
4710-057 braga, portugal
(+351) 253 604355
office# math-3.64