Any time writing in pure python causes a segfault is a serious bug. Glancing briefly at the code, I have a few ideas for what might have caused it: I'll take a more detailed look in an hour or two.
Regardless of what's causing the crash, I'd suggest you use the methods described at http://www.sagemath.org/doc/reference/coercion.html rather than implementing your own __call__, _coerce_impl on the parent. It's also a good idea to use parent() rather than setting self._parent = A directly in your __init__ method. I'll get back to you soon with (hopefully) a reason why it's crashing. David On Wed, Dec 16, 2009 at 10:09 AM, Daniel Bump <b...@match.stanford.edu>wrote: > > I will explain how to make sage have a segmentation fault > with the following alarming message: > > ------------------------------------------------------------ > 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). > ------------------------------------------------------------ > > Apply the following patch to sage-4.3.rc0: > t > http://sporadic.stanford.edu/bump/patches/coerce_actions_segfault.patch > > This creates a file called sage/algebras/iwahori.py. Eventually > it will make the Iwahori Hecke algebra of a Weyl group but > at the moment it just makes the group algebra. You can do > stuff like this: > > sage: H = WeylGroupAlgebra("B3") > sage: [T1,T2,T3]=H.simple_reflections() > sage: (T2*T3)^4 > 1 > sage: (T1*T2)^3 > 1 > > Unfortunately you can get a crash by evaluating 2*T1. > > A backtrace with gdb shows frames in coerce_actions.c, > coerce.c, parent.c, parent_old.c and element.c, all > in sage/structure/ with corresponding cython files *.pyx. > > To get the backtrace, run sage -gdb, make it crash, then > type bt at the gdb prompt. > > Examination of the backtrace led to the following more > direct way of causing the crash: > > sage: WeylGroupAlgebra("A2").get_action(ZZ) > > I can probably work around this by writing a > new _get_action_ method, so maybe this is not > such a severe bug. But I am reporting it here. > > If it is deemed severe I will make a trac ticket. > > Daniel Bump > > -- > To post to this group, send an email to sage-devel@googlegroups.com > To unsubscribe from this group, send an email to > sage-devel+unsubscr...@googlegroups.com<sage-devel%2bunsubscr...@googlegroups.com> > For more options, visit this group at > http://groups.google.com/group/sage-devel > URL: http://www.sagemath.org > -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
