#13882: Deal with a trivial case in dlx_solver
-----------------------------+----------------------------------------------
Reporter: SimonKing | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-5.6
Component: combinatorics | Keywords: dlx_solver nr_columns
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
-----------------------------+----------------------------------------------
Using Sage's debug version from #13864, the following crashes:
{{{
sage: from sage.combinat.matrices.dancing_links import dlx_solver
sage: x = dlx_solver([])
python: sage/combinat/matrices/dancing_links_c.h:217: void
dancing_links::setup_columns(): Assertion `nr_columns > 0' failed.
Program received signal SIGABRT, Aborted.
0x00007ffff6d95d95 in raise () from /lib64/libc.so.6
(gdb) bt
#0 0x00007ffff6d95d95 in raise () from /lib64/libc.so.6
#1 0x00007ffff6d972ab in abort () from /lib64/libc.so.6
#2 0x00007ffff6d8e8fe in __assert_fail_base () from /lib64/libc.so.6
#3 0x00007ffff6d8e9a2 in __assert_fail () from /lib64/libc.so.6
#4 0x00007fffc3e38dc2 in dancing_links::setup_columns
(this=0x7fffc2cc3e90) at sage/combinat/matrices/dancing_links_c.h:217
#5 0x00007fffc3e39101 in dancing_links::add_rows (this=0x7fffc2cc3e90,
rows=...) at sage/combinat/matrices/dancing_links_c.h:268
#6 0x00007fffc3e3251d in
__pyx_pf_4sage_8combinat_8matrices_13dancing_links_20dancing_linksWrapper_14add_rows
(__pyx_v_self=0x7fffc2cc3e70, __pyx_v_rows=0x7ffff2375498)
at sage/combinat/matrices/dancing_links.cpp:2666
#7 0x00007fffc3e31c18 in
__pyx_pw_4sage_8combinat_8matrices_13dancing_links_20dancing_linksWrapper_15add_rows
(__pyx_v_self=0x7fffc2cc3e70, __pyx_v_rows=0x7ffff2375498)
at sage/combinat/matrices/dancing_links.cpp:2464
#8 0x00007ffff7a21151 in PyCFunction_Call (func=0x7fffc2a0da38,
arg=0x7fffefaad920, kw=0x0) at Objects/methodobject.c:101
#9 0x00007ffff79be33e in PyObject_Call (func=0x7fffc2a0da38,
arg=0x7fffefaad920, kw=0x0) at Objects/abstract.c:2529
#10 0x00007fffc3e30130 in
__pyx_pf_4sage_8combinat_8matrices_13dancing_links_20dancing_linksWrapper_2__cinit__
(__pyx_v_self=0x7fffc2cc3e70, __pyx_v_rows=0x7ffff2375498)
at sage/combinat/matrices/dancing_links.cpp:2010
#11 0x00007fffc3e2fe79 in
__pyx_pw_4sage_8combinat_8matrices_13dancing_links_20dancing_linksWrapper_3__cinit__
(__pyx_v_self=0x7fffc2cc3e70, __pyx_args=0x7fffefab74c0, __pyx_kwds=0x0)
at sage/combinat/matrices/dancing_links.cpp:1946
#12 0x00007fffc3e33b28 in
__pyx_tp_new_4sage_8combinat_8matrices_13dancing_links_dancing_linksWrapper
(t=0x7fffc4045000
<__pyx_type_4sage_8combinat_8matrices_13dancing_links_dancing_linksWrapper>,
a=0x7fffefab74c0, k=0x0) at
sage/combinat/matrices/dancing_links.cpp:3037
#13 0x00007ffff7a4bfe3 in type_call (type=0x7fffc4045000
<__pyx_type_4sage_8combinat_8matrices_13dancing_links_dancing_linksWrapper>,
args=0x7fffefab74c0, kwds=0x0) at Objects/typeobject.c:721
#14 0x00007ffff79be33e in PyObject_Call (func=0x7fffc4045000
<__pyx_type_4sage_8combinat_8matrices_13dancing_links_dancing_linksWrapper>,
arg=0x7fffefab74c0, kw=0x0) at Objects/abstract.c:2529
#15 0x00007fffc3e32f12 in
__pyx_pf_4sage_8combinat_8matrices_13dancing_links_dlx_solver
(__pyx_self=0x0, __pyx_v_rows=0x7ffff2375498) at
sage/combinat/matrices/dancing_links.cpp:2888
#16 0x00007fffc3e32e33 in
__pyx_pw_4sage_8combinat_8matrices_13dancing_links_1dlx_solver
(__pyx_self=0x0, __pyx_v_rows=0x7ffff2375498) at
sage/combinat/matrices/dancing_links.cpp:2852
#17 0x00007ffff7ac6943 in call_function (pp_stack=0x7fffffffaab0, oparg=1)
at Python/ceval.c:4009
#18 0x00007ffff7ac16ba in PyEval_EvalFrameEx (f=0x2f17a50, throwflag=0) at
Python/ceval.c:2666
#19 0x00007ffff7ac40aa in PyEval_EvalCodeEx (co=0x7ffff6a9b460,
globals=0x9b0080, locals=0x9b0080, args=0x0, argcount=0, kws=0x0,
kwcount=0, defs=0x0, defcount=0, closure=0x0) at Python/ceval.c:3253
#20 0x00007ffff7ab9a88 in PyEval_EvalCode (co=0x7ffff6a9b460,
globals=0x9b0080, locals=0x9b0080) at Python/ceval.c:667
#21 0x00007ffff7ac9693 in exec_statement (f=0x297f8c0,
prog=0x7ffff6a9b460, globals=0x9b0080, locals=0x9b0080) at
Python/ceval.c:4718
#22 0x00007ffff7abde26 in PyEval_EvalFrameEx (f=0x297f8c0, throwflag=0) at
Python/ceval.c:1880
#23 0x00007ffff7ac40aa in PyEval_EvalCodeEx (co=0x7ffff280c720,
globals=0x909bf0, locals=0x0, args=0x297f150, argcount=2, kws=0x297f160,
kwcount=0, defs=0x0, defcount=0, closure=0x0)
at Python/ceval.c:3253
#24 0x00007ffff7ac71b5 in fast_function (func=0x7ffff235b450,
pp_stack=0x7fffffffb430, n=2, na=2, nk=0) at Python/ceval.c:4117
#25 0x00007ffff7ac6d76 in call_function (pp_stack=0x7fffffffb430, oparg=1)
at Python/ceval.c:4042
#26 0x00007ffff7ac16ba in PyEval_EvalFrameEx (f=0x297efa0, throwflag=0) at
Python/ceval.c:2666
...
}}}
My guess is that one can check whether the input is empty, dealing with
that special case separately. Alternatively, if empty columns are
acceptable, the assertion should be `nr_columns >= 0` rather than
`nr_columns > 0`.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13882>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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