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May 20th, 2007, 07:19 PM  #1 
Newbie Joined: May 2007 Posts: 13 Thanks: 0  Supersingular elliptic curve question
I need help in interpreting the definition of a supersingular elliptic curve. Namely, what a "cubic equation of the form f(w,x,y)=0" means. A definition can be found here: http://planetmath.org/encyclopedia/Supersingular.html What I am having trouble is what the variable w is. In context of my problem, I have a curve in Weierstrass form and want to know what the cubic equation as referred to above corresponds to. I'm assuming that x and y are just the variables found in an elliptic curve. Thanks in advance for the help. I'll post back here if I find out an answer before there are any replies. 
May 20th, 2007, 09:40 PM  #2 
Newbie Joined: May 2007 Posts: 13 Thanks: 0 
f(w,x,y)=0 is the elliptic curve in normal form.

May 30th, 2007, 03:00 AM  #3  
Member Joined: Dec 2006 Posts: 39 Thanks: 0  Re: Supersingular elliptic curve question Quote:
I wrote my thesis on singular and supersingular curves. There I show that a curve over a perfect field of char. p is supersingular iff it fulfills several equivalent conditions. One of the nicest ones is that its invariant differential is exact, but others are: An elliptic curve E over a perfect field of char. p is supersingular iff: 1) Its invariant differential is exact, iff: 2) E[p] = 0, where E[p] = { x in E / px = 0}, iff: 3) The Froebenius map P_p is purely inseparable, iff: 4) The map [p]: E > E is purely inseparable, iff: 5) the coefficient of x^(p1) in f(x)^(p1)/2, when E: y^2 = f(x) and f(x) is a cubic in x with different roots. You may want to check Silverman's book on elliptic cureves... Reagrds Tonio  
June 2nd, 2007, 11:19 AM  #4 
Newbie Joined: May 2007 Posts: 13 Thanks: 0 
Thanks, but the ultimate criterion I used was a theorem from Lang's Elliptic functions which basically states that if a prime p stays inert from a rational to a quadratic field and an elliptic curve E has complex multiplication by an order of the quadratic field, then E mod p is supersingular. This fit perfectly with what I was doing and I didn't want to have to define things like invariant differential. I appreciate the help though. Frank 

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