cliquer does not like the empty graph

[sagetrac-azi]

Stupid corner case but still worth fixing. Asking for the clique number of the empty graph blows Sage off.

sage: graphs.EmptyGraph().clique_number()
cliquer file graph.c: line 31: assertion failed: (n>0)
------------------------------------------------------------------------
/home/azi/sage-5.10.beta1/local/lib/libcsage.so(print_backtrace+0x31)[0x7fa2060bc7a0]
/home/azi/sage-5.10.beta1/local/lib/libcsage.so(sigdie+0x37)[0x7fa2060bc939]
/home/azi/sage-5.10.beta1/local/lib/libcsage.so(sage_signal_handler+0x15d)[0x7fa2060bc14b]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x10060)[0x7fa20a089060]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x35)[0x7fa2096813e5]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x17b)[0x7fa209684b4b]
/home/azi/sage-5.10.beta1/local/lib/libcliquer.so(+0xa38a)[0x7fa1dc2be38a]
/home/azi/sage-5.10.beta1/local/lib/python2.7/site-packages/sage/graphs/cliquer.so(+0x39a6)[0x7fa1dc4cb9a6]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x5999)[0x7fa20a38aa19]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCode+0x32)[0x7fa20a38bad2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x4749)[0x7fa20a3897c9]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x45ed)[0x7fa20a38966d]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x822)[0x7fa20a38b9a2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyEval_EvalCode+0x32)[0x7fa20a38bad2]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyRun_FileExFlags+0xaa)[0x7fa20a3ad46a]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(PyRun_SimpleFileExFlags+0xed)[0x7fa20a3adead]
/home/azi/sage-5.10.beta1/local/lib/libpython2.7.so.1.0(Py_Main+0xc22)[0x7fa20a3c3992]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7fa20966c30d]
python[0x4006d1]
------------------------------------------------------------------------
Attaching gdb to process id 13317.
GNU gdb (Ubuntu/Linaro 7.3-0ubuntu2) 7.3-2011.08
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>.
(gdb) Hangup detected on fd 0
error detected on stdin

Your system GDB is an old version that does not work with pipes
Install the gdb spkg (sage -f gdb) for enhanced tracebacks.
------------------------------------------------------------------------
Unhandled SIGABRT: An abort() 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.
------------------------------------------------------------------------
/usr/local/bin/sage: line 135: 13317 Aborted                 "$SAGE_ROOT/spkg/bin/sage" "$@"

Simply checking if the supplied graph is empty is going to fix this for sure.

CC: @nathanncohen

Component: graph theory

Author: Nico Van Cleemput

Reviewer: Nathann Cohen

Merged: sage-5.10.rc1

Issue created by migration from https://trac.sagemath.org/ticket/14525

[nathanncohen]

comment:1

I am an idiot -_-

#10756

Nathann

[nvcleemp]

comment:2

Nobody seemed to be working on this, so I quickly fixed it. I also fixed the method to get all maximum cliques.

I didn't add my name to the authors, since this is just a minor bug fix. I don't know the policy on this. I'm sure that I can be found through the versioning system, if at some point I need to be blamed for introducing a bug.

[nathanncohen]

comment:3

Why would you return [g.vertices()] when g.order() is 0 ? O_o

Wouldn't return [[]] do ? O_o

And even short bugfixes have authors, and even there the author is the one who writes the patch. Soooooooooooooooo :-)

Nathann

[nvcleemp]

comment:4

I actually copied the patch for #10756, which returns g.vertices() as a maximum clique when g.order() is 0. I'd be happy to change it to [[]], but maybe then I should also change the other method to return [] just to be consistent for all three methods.

[nathanncohen]

comment:5

If you can, it would be nice indeed :-)

Nathann

[nvcleemp]

As requested

[nvcleemp]

comment:6

Attachment: trac_14525_cliquer_empty.patch.gz

btw, the tests actually test methods different from these functions but which use those functions. I guessed this was OK, because that was also the way it was done for max_clique().

[nathanncohen]

comment:7

Hmmmmmm... It is correct most of the time, because sage -coverage notices that the function's name is the same, but that does not work for all_max_clique ^^;

~/sage/sage/graphs$ sage -coverage cliquer.pyx 
------------------------------------------------------------------------
SCORE cliquer.pyx: 100.0% (4 of 4)

Possibly wrong (function name doesn't occur in doctests):
     * line 95: def all_max_clique(graph)
------------------------------------------------------------------------

I just uploaded a small patch that fixes that. If you agree with it, then you can set this ticket to positive_review :-)

Nathann

[nathanncohen]

Reviewer: Nathann Cohen

[nathanncohen]

Author: Nico Van Cleemput

[nvcleemp]

comment:8

Attachment: trac_14525-rev.patch.gz

OK, looks ok and works for me.

[jdemeyer]

Merged: sage-5.10.rc1