Given a cuspidal, classical eigenform $f\in S_2(\Gamma_0(N))$ of weight $2$ and with $\mathbf{Q}$-coefficients is there a way of describing the set $J_f$ of $j$-invariants of the elliptic curves lying in the isogeny class determined by $f$?

Has this question been looked at? Thanks.

  • 2
    $\begingroup$ Compute the periods from a $q$-expansion by this projecteuclid.org/euclid.em/1047649997 Then compute $j(\tau)$ and recognize it rationally. Then find all isogenous curves. For the last two steps, see Cremona's book (which also gives the first, but not so refined). $\endgroup$ – GuestPoster Jun 5 '15 at 9:18
  • $\begingroup$ Is there an actual question here? I'm confused. $\endgroup$ – user74597 Jun 14 '15 at 18:00
  • $\begingroup$ I think the question is there. I agree that's somewhat vague. I will soon retire it. $\endgroup$ – Tommaso Centeleghe Jun 24 '15 at 9:45

Didn't John Cremona write a book about this question? (And then compute all such elliptic curves for $N$ less than a bizillion or so?)


  • $\begingroup$ Also, Cremona's tables are available in searchable form interact.sagemath.org/Tables/cremona/INDEX.html SAGE implements modular symbols doc.sagemath.org/html/en/reference/modsym/index.html , which is the main toolkit used for the computation. I haven't found a one line command in SAGE to just do this, but I expect one exists; this is dead in the center of William Stein's interests. $\endgroup$ – David E Speyer Jun 5 '15 at 3:33
  • $\begingroup$ I might suggest wstein.org/books/modform/stein-modform.pdf as a more modern updating of Cremona. The specific question is answered in Section 10.6 $\endgroup$ – David E Speyer Jun 5 '15 at 3:40
  • $\begingroup$ @DavidSpeyer You should browse Cremona's tables on the LMFDB website lmfdb.org/EllipticCurve/Q, the link you provide is obsolete. $\endgroup$ – Aurel Jun 5 '15 at 8:50
  • $\begingroup$ Thank you all for your answers. I guess what I had in mind was a characterization of $J_f$ starting from $f$, and not necessarily a concrete procedure to calculate $J_f$. $\endgroup$ – Tommaso Centeleghe Jun 9 '15 at 8:48

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