finding modular symbols space of given sign attached to modular abelian variety is broken in some cases

[williamstein]

wstein@sage:~$ sage
----------------------------------------------------------------------
| Sage Version 4.8, Release Date: 2012-01-20                         |
| Type notebook() for the GUI, and license() for information.        |
----------------------------------------------------------------------
sage: J = J0(188)[0]
sage: J.modular_symbols(1)
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)

/home/wstein/<ipython console> in <module>()

/usr/local/share/sage-4.8/local/lib/python2.6/site-packages/sage/modular/abvar/abvar.pyc in modular_symbols(self, sign)
   3773         M = self._modular_symbols().modular_symbols_of_sign(sign)
   3774         if (sign != 0 and M.dimension() != self.dimension()) or (sign == 0 and M.dimension() != 2*self.dimension()):
-> 3775             raise RuntimeError, "unable to determine sign (=%s) space of modular symbols"%sign
   3776         return M
   3777     

RuntimeError: unable to determine sign (=1) space of modular symbols

This is also broken in sage-5.0.beta3. I have some reason to believe this worked fine a year ago...

Component: modular forms

Issue created by migration from https://trac.sagemath.org/ticket/12566

[williamstein]

comment:1

I'm being stupid -- the given space isn't new, so the space isn't even defined. Stupid.