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 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