On 21 April 2014 13:58, Irene <[email protected]> wrote:
> I forgot to write what is repsq():

You could use the builtin function power_mod:

sage: power_mod?
Type:       function
String Form:<function power_mod at 0x1f78668>
File:       
/usr/local/sage/sage-6.1.1/local/lib/python2.7/site-packages/sage/rings/arith.py
Definition: power_mod(a, n, m)
Docstring:
   The n-th power of a modulo the integer m.


> #repsq(a,n) computes a^n
> def repsq(a,n):
>     B = Integer(n).binary()
>     C=list(B)
>     k=len(B)-1
>     bk=a
>     i=1
>     while i <= k:
>         if C[i]=="1":
>             bk=(bk^2)*a
>         else:
>             bk=bk^2
>         i=i+1
>     return bk
>
>
> On Monday, April 21, 2014 11:48:10 AM UTC+2, Irene wrote:
>>
>> Hello,
>> I have the following defined:
>>
>> p=3700001
>> Fp=GF(p)
>> E=EllipticCurve([Fp(3),Fp(5)])
>> j_inv=E.j_invariant()
>> l=13#Atkin prime
>> n=((l-1)/2).round()
>> r=2# Phi_13 factorize in factors of degree 2
>> s=12#Psi_13 factorize in factors of degree 12
>> Fps=GF(repsq(p,s),'a')
>> a=Fps.gen()
>> Fpr=GF(repsq(p,r),'b')
>> b=Fpr.gen()
>> FFps.<X>=PolynomialRing(Fps)
>> FFpr.<x>=PolynomialRing(Fpr)
>> EP=x^6 + (973912*b + 2535329)*x^5 + (416282*b + 3608920)*x^4 + (686636*b +
>> 908282)*x^3 + (2100014*b + 2063451)*x^2 + (2563113*b + 751714)*x + 2687623*b
>> + 1658379
>> A1.<theta>=Fpr.extension(EP)
>>
>> and now I want to "add" to A1 the square root of theta^3+3*theta+5.
>> The problem is that when I consider the following:
>>
>> gamma2=theta^3+3*theta+5
>> AA1.<xbar>=PolynomialRing(A1)
>> AA.<gamma>=A1.extension(xbar^2-gamma2)
>> (xbar^2-gamma2).roots(AA,multiplicities=False)
>>
>> it gives me a NotImplementedError. Any idea? Thank you in advance.
>> Irene
>>
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