#12339: Free Groups
------------------------------------------------------------------+---------
Reporter: mmarco |
Owner: joyner
Type: enhancement |
Status: needs_work
Priority: major |
Milestone: sage-5.5
Component: group theory |
Resolution:
Keywords: free groups, finitely presented groups, braids | Work
issues:
Report Upstream: N/A |
Reviewers: Volker Braun
Authors: Miguel Marco | Merged
in:
Dependencies: #6391, #13687, #13588 |
Stopgaps:
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Comment (by jhpalmieri):
For what it's worth, I get the same error [comment:61 as above] on
sage.math. A simpler example:
{{{
sage: G.<e0> = FreeGroup()
sage: relns_G = [e0^2]
sage: H.<e0, e1> = FreeGroup()
sage: relns_H = [e0^2, e1]
sage: G2 = G / relns_G
sage: H2 = H / relns_H
sage: G2.simplified()
Finitely presented group < e0 | e0^2 >
sage: H2.simplified()
Exception RuntimeError: "Error, no method found! For debugging hints type
?Recovery from NoMethodFound\nError, no 1st choice method found for `<' on
2 arguments\n" in 'sage.libs.gap.util.error_handler' ignored
/scratch/palmieri/sage-5.5.rc0/local/lib/libcsage.so(print_backtrace+0x31)[0x7f5a11f63207]
/scratch/palmieri/sage-5.5.rc0/local/lib/libcsage.so(sigdie+0x14)[0x7f5a11f63239]
/scratch/palmieri/sage-5.5.rc0/local/lib/libcsage.so(sage_signal_handler+0x216)[0x7f5a11f62e16]
/lib/libpthread.so.0[0x7f5a171797d0]
[0x7f58e53e47d0]
------------------------------------------------------------------------
Unhandled SIGSEGV: A segmentation fault occurred in Sage.
This probably occurred because a *compiled* component of Sage has a bug
in it and 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.
------------------------------------------------------------------------
}}}
It looks like the issue is using the same generator names for `G` and `H`:
if I change it so `H` is defined by `H.<f0, f1> = FreeGroup()`, I don't
get this problem. I think this needs to be dealt with, and a doctest needs
to be added verifying that it has been dealt with.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12339#comment:63>
Sage <http://www.sagemath.org>
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