|Bill Allombert on Sat, 09 Jun 2012 00:05:37 +0200|
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|Re: ell from j|
On Fri, Jun 08, 2012 at 09:04:57PM +0100, John Cremona wrote: > I wrote a similar function for Sage, called EllipticCurve_from_j, but > it is not normally called directly, rather one does EllipticCurve > (j=...). Can gp use named parameters, so you could do ellinit(j=...)? > > The Sage function has special cases for characteristics 2 and 3, and > also over Q it gives a minimal quadratic twist. The computation of the minimal quadratic twist requires the factorisation of j/(1728-j) which can be large, so this would change the complexity of the function. Cheers, Bill.