|Bill Allombert on Wed, 11 May 2005 18:25:43 +0200|
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|Re: Proposed elldata database at the PARI workshop|
On Mon, May 09, 2005 at 08:52:49PM +0200, Bill Allombert wrote: > On Wed, May 04, 2005 at 11:03:34AM +0200, Jeroen Demeyer wrote: > > It would be very cool to have a "reverse lookup" feature: > > > > Given a curve E, there should be a command ellidentify(E) giving back > > the curve number and a matrix defining the isomorphism with the curve in > > Cremona's list. > > This is a good idea! > I think it is easy to implement with ellglobalred() and a elllist() > routine. OK, so I have a tentative implementation. It includes 3 functions: ellbyname(name): retrieve a curve by its name. ellcondlist(conductor): retrieve all curves of a given conductor. ellidentify(curve): retrieve the name of the curve and the base change. and an elldata package that include all curves from John Cremona database upto conductor 39999 (based on a first version by William Stein). Now, three questions: 1) A better name for ellcondlist and ellbyname? 2) Should ellbyname by available directly under GP or only through ellinit() ? 3) Should we store more information in the tables than just the names and the coefficients? if yes, how we will use them ? Cheers, Bill.