id,summary,reporter,owner,description,type,status,priority,milestone,component,resolution,keywords,cc,merged,author,reviewer,upstream,work_issues,branch,commit,dependencies,stopgaps
31317,eclib interface uses bad default value for elliptic curve modular symbols,John Cremona,,"This was reported to me by Chris Wuthrich in December 2019, and by Barry Mazur and Karl Rubin a few days ago. I originally thought that there was a bug in eclib, but it turns out that the only bug is that the default value of certain parameters is too small for the cases they were interested in. I will post a 2-line patch to increase this. It has to be a 2-line patch, not 1, since the current eclib interfae does not expose the relevant parameter to Sage at all currently.
Here are two example. Wuthrich's (takes a little while as the conductor is 87416):
{{{
sage: E = EllipticCurve([49,-49])
sage: me = E.modular_symbol(implementation=""eclib"")
sage: me(1/8)
10/17
sage: mn = E.modular_symbol(implementation=""num"")
sage: mn(1/8)
1/2
}}}
and Mazur's:
{{{
sage: E = EllipticCurve('1590g1')
sage: ms = E.modular_symbol()
sage: [ms(a/5) for a in [1..4]]
[1001/153, -1001/153, -1001/153, 1001/153]
sage: ms = E.modular_symbol(implementation='num')
sage: [ms(a/5) for a in [1..4]]
[13/2, -13/2, -13/2, 13/2]
}}}
In both cases, after my patch the 'eclib' values agree with the numerical values.",defect,closed,major,sage-9.3,elliptic curves,fixed,elliptic curve modular symbol,wuthrich,,John Cremona,Chris Wuthrich,N/A,,2ab86ef72a3ddc7341ed76e4dc0dbd0ce7ee0162,2ab86ef72a3ddc7341ed76e4dc0dbd0ce7ee0162,,