On Nov 21, 4:56 am, Alex Ghitza <[EMAIL PROTECTED]> wrote:
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Hi Alex,
>
> Hi,
>
> I've been playing with spaces of modular symbols over finite fields, and
> I ran into two issues that seem to be separate (they're tickets #1231
> and #1232 now):
>
> 1. doing
>
> ModularSymbols(1,8,0,GF(3)).simple_factors()
>
> gives
>
> - ------------------------------------------------------------
> Unhandled SIGSEGV: A segmentation fault occured in SAGE.
> This probably occured because a *compiled* component
> of SAGE has a bug in it (typically accessing invalid memory)
> or is not properly wrapped with _sig_on, _sig_off.
> You might want to run SAGE under gdb with 'sage -gdb' to debug this.
> SAGE will now terminate (sorry).
> - ------------------------------------------------------------
While I cannot reproduce this particular problem on sage.math, of the
other 4 examples you give the first one also segfaults on sage.math
with 2.8.13.rc1. So I do have something do debug this from. I will see
if anything pops up with valgrind.
Cheers,
Michael
>
> The same phenomenon occurs over other finite fields.
>
> 2. doing
>
> ModularSymbols(1,6,0,GF(2)).simple_factors()
>
> gives
>
> -
> ---------------------------------------------------------------------------
> <type 'exceptions.AssertionError'> Traceback (most recent call last)
>
> /home/ghitza/sage/<ipython console> in <module>()
>
> /opt/sage/local/lib/python2.5/site-packages/sage/modular/modsym/space.py
> in simple_factors(self)
> 996 ASSUMPTION: self is a module over the anemic Hecke algebra.
> 997 """
> - --> 998 return [S for S,_ in self.factorization()]
> 999
> 1000 def star_eigenvalues(self):
>
> /opt/sage/local/lib/python2.5/site-packages/sage/modular/modsym/ambient.py
> in factorization(self)
> 1064 D = sage.structure.all.Factorization(D, cr=True)
> 1065 assert r == s, "bug in factorization -- self has
> dimension %s, but sum of dimensions of factors is %s\n%s"%(
> - -> 1066 r, s, D)
> 1067 self._factorization = D
> 1068 return self._factorization
>
> <type 'exceptions.AssertionError'>: bug in factorization -- self has
> dimension 2, but sum of dimensions of factors is 3
> (Modular Symbols subspace of dimension 1 of Modular Symbols space of
> dimension 2 for Gamma_0(1) of weight 6 with sign 0 over Finite Field of
> size 2) *
> (Modular Symbols subspace of dimension 1 of Modular Symbols space of
> dimension 2 for Gamma_0(1) of weight 6 with sign 0 over Finite Field of
> size 2) *
> (Modular Symbols subspace of dimension 1 of Modular Symbols space of
> dimension 2 for Gamma_0(1) of weight 6 with sign 0 over Finite Field of
> size 2)
> - -------------------------------------------------------------------------
>
> I have not looked at the implementation, but as far as I know the
> algorithms with modular symbols work directly over the field of
> definition, so it seems unlikely that this is related to the problem
> that Ifti raised a few days ago, about reduction of coefficients modulo
> prime ideals.
>
> Best,
> Alex
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