1 optional gurobi doctest failing

[slabbe]

Using 8.6.beta1 with Gurobi installed and available in Sage (as explained ​here), the command

sage -t --optional=sage,external src/sage/numerical/backends/gurobi_backend.pyx

gives

Using --optional=external,memlimit,sage
External software to be detected: cplex,ffmpeg,graphviz,gurobi,imagemagick,internet,latex,macaulay2,magma,maple,mathematica,matlab,octave,pandoc,scilab
Doctesting 1 file.
sage -t src/sage/numerical/backends/gurobi_backend.pyx
**********************************************************************
File "src/sage/numerical/backends/gurobi_backend.pyx", line 50, in sage.numerical.backends.gurobi_backend.GurobiBackend
Failed example:
    TestSuite(p.get_backend()).run(skip="_test_pickling")         # optional - Gurobi
Expected nothing
Got:
    Failure in _test_copy:
    Traceback (most recent call last):
      File "/home/slabbe/GitBox/sage/local/lib/python2.7/site-packages/sage/misc/sage_unittest.py", line 296, in run
        test_method(tester = tester)
      File "sage/numerical/backends/generic_backend.pyx", line 1255, in sage.numerical.backends.generic_backend.GenericBackend._test_copy (build/cythonized/sage/numerical/backends/generic_backend.c:14740)
        self._do_test_problem_data(tester, cp)
      File "sage/numerical/backends/generic_backend.pyx", line 1229, in sage.numerical.backends.generic_backend.GenericBackend._do_test_problem_data (build/cythonized/sage/numerical/backends/generic_backend.c:14457)
        assert_equal_problem_data(method)
      File "sage/numerical/backends/generic_backend.pyx", line 1226, in sage.numerical.backends.generic_backend.GenericBackend._do_test_problem_data.assert_equal_problem_data (build/cythonized/sage/numerical/backends/generic_backend.c:13727)
        tester.assertEqual(getattr(self, method)(), getattr(cp, method)(),
      File "/home/slabbe/GitBox/sage/local/lib/python2.7/unittest/case.py", line 513, in assertEqual
        assertion_func(first, second, msg=msg)
      File "/home/slabbe/GitBox/sage/local/lib/python2.7/unittest/case.py", line 506, in _baseAssertEqual
        raise self.failureException(msg)
    AssertionError: problem_name does not match
    ------------------------------------------------------------
    Failure in _test_copy_does_not_share_data:
    Traceback (most recent call last):
      File "/home/slabbe/GitBox/sage/local/lib/python2.7/site-packages/sage/misc/sage_unittest.py", line 296, in run
        test_method(tester = tester)
      File "sage/numerical/backends/generic_backend.pyx", line 1265, in sage.numerical.backends.generic_backend.GenericBackend._test_copy_does_not_share_data (build/cythonized/sage/numerical/backends/generic_backend.c:14947)
        self._do_test_problem_data(tester, cpcp)
      File "sage/numerical/backends/generic_backend.pyx", line 1229, in sage.numerical.backends.generic_backend.GenericBackend._do_test_problem_data (build/cythonized/sage/numerical/backends/generic_backend.c:14457)
        assert_equal_problem_data(method)
      File "sage/numerical/backends/generic_backend.pyx", line 1226, in sage.numerical.backends.generic_backend.GenericBackend._do_test_problem_data.assert_equal_problem_data (build/cythonized/sage/numerical/backends/generic_backend.c:13727)
        tester.assertEqual(getattr(self, method)(), getattr(cp, method)(),
      File "/home/slabbe/GitBox/sage/local/lib/python2.7/unittest/case.py", line 513, in assertEqual
        assertion_func(first, second, msg=msg)
      File "/home/slabbe/GitBox/sage/local/lib/python2.7/unittest/case.py", line 506, in _baseAssertEqual
        raise self.failureException(msg)
    AssertionError: problem_name does not match
    ------------------------------------------------------------
    The following tests failed: _test_copy, _test_copy_does_not_share_data
**********************************************************************
1 item had failures:
   1 of   3 in sage.numerical.backends.gurobi_backend.GurobiBackend
    [207 tests, 1 failure, 0.14 s]
----------------------------------------------------------------------
sage -t src/sage/numerical/backends/gurobi_backend.pyx  # 1 doctest failed
----------------------------------------------------------------------
Total time for all tests: 0.2 seconds
    cpu time: 0.1 seconds
    cumulative wall time: 0.1 seconds
External software detected for doctesting: gurobi

[slabbe]

This failure was first seen in 8.6.beta0 and was not present in 8.5.beta5. Looking at what was merged in 8.5.beta6 and 8.6.beta0, the first natural hypothesis would be that this failure was introduced in #24740 merged in 8.6.beta0.

[embray]

Probably so; I don't think we've tested against all optional packages (though perhaps that's just something I'm going to start doing, at least with all the optional packages I can successfully install on a give platform...).

[embray]

I see now; this is not even an optional package, but an external dependency of proprietary software :( Nevertheless, the issue seems straightforward...

[embray]

On second thought, looking at the relevant code changes, it's not at all clear what would have changed to result in this difference, especially on Python 2. It's possible #24740 is not even related.

It would help if you could do some examples manually, since the output from the test suite is not very helpful (it would be better if it showed the actual difference).

What does it show if you do:

sage: from copy import copy
sage: p = MixedIntegerLinearProgram(solver="Gurobi")
sage: b = p.get_backend()
sage: b.problem_name()
???
sage: b2 = copy(b)
sage: b2.problem_name()
???

That seems to be the test this is doing, though I'm not positive if that's all that's needed to reproduce the failure, and without access to Gurobi I can't easily debug it :(

[slabbe]

I have access to two machines with Gurobi installed, one running 8.5.beta4 and the other running 8.6.rc0:

┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 8.5.beta4, Release Date: 2018-11-18               │
│ Using Python 2.7.15. Type "help()" for help.                       │
└────────────────────────────────────────────────────────────────────┘
sage: from copy import copy
sage: p = MixedIntegerLinearProgram(solver="Gurobi")
sage: b = p.get_backend()
sage: b.problem_name()
''
sage: b2 = copy(b)
sage: b2.problem_name()
''

┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 8.6.rc0, Release Date: 2019-01-03                 │
│ Using Python 2.7.15. Type "help()" for help.                       │
└────────────────────────────────────────────────────────────────────┘
sage: from copy import copy
sage: p = MixedIntegerLinearProgram(solver="Gurobi")
sage: b = p.get_backend()
sage: b.problem_name()
''
sage: b2 = copy(b)
sage: b2.problem_name()
'(null)_copy'

[slabbe]

Replying to embray:

I see now; this is not even an optional package, but an external dependency of proprietary software :(

"For University Users: If you are a student, faculty, or staff member at a recognized degree-granting institution, you may be eligible for a free, full-featured, no-size limit, academic version of Gurobi."

Source: ​http://www.gurobi.com/academia/academia-center

[embray]

Thanks--all of the above is useful info.

[embray]

I haven't tested, but this should fix it. (You were right of course by it being introduced by #24740; not surprising though the reason was a bit subtle.)

---

New commits:

​8cd23e4

Trac #26999: fix GurobiBackend.problem_name()

[slabbe]

It fixes the issue.

[embray]

Retarging tickets optimistically to the next milestone. If you are responsible for this ticket (either its reporter or owner) and don't believe you are likely to complete this ticket before the next release (8.7) please retarget this ticket's milestone to sage-pending or sage-wishlist.