More tests for common MIP TestSuite: add_col, solve; some fixes for backends

[mkoeppe]

Split out from #20323.

This patch adds new _test methods for add_col, solve, and for #18572 (but disabled for CVXOPT, where it fails). To make the new test methods happy,

• implement add_col for Gurobi;
• fix the implementation of add_col for COIN;
• fix Gurobi's treatment of unbounded variables;
• fix CPLEX unboundedness detection.

If anyone at all cares about the CVXOPT backend, perhaps they could fix it?

From dimpase:

I recall asking how one deals with different backends producing different, albeit equivalent, outputs. E.g. some of them would even introduce extra variables for some constraints (see e.g. ​ ​http://trac.sagemath.org/ticket/13148#comment:2). Some backends assign names to constraints automatically.

[mkoeppe]

Branch is on top of #20323.

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Last 10 new commits:

​d93b798	Change from mutating instance _test methods to class methods
​94a4ac5	New method _test_ncols_nonnegative
​2251125	GenericBackend: Remove failing _test methods from this ticket to make the patchbot and its friends happy
​934456f	Revert "GenericBackend: Remove failing _test methods from this ticket to make the patchbot and its friends happy"
​a85cada	_test_copy: New
​8070754	_test_copy_does_not_share_data: New
​d04b270	Test backend.copy() rather than copy(backend)
​480a71b	test_copy_some_mips: New
​3b49831	Add _test_solve_trac_18572 (autogenerated)
​e5e6227	_test_solve_trac_18572: Replace float integers by integers to make test suitable for PPL backend

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. Last 10 new commits:

​48b9fe5	Change from mutating instance _test methods to class methods
​5394729	New method _test_ncols_nonnegative
​7138fa0	GenericBackend: Remove failing _test methods from this ticket to make the patchbot and its friends happy
​9f4f25c	Revert "GenericBackend: Remove failing _test methods from this ticket to make the patchbot and its friends happy"
​8421950	_test_copy: New
​3f0578b	_test_copy_does_not_share_data: New
​f5b42b8	Test backend.copy() rather than copy(backend)
​f21ce7c	test_copy_some_mips: New
​21abe28	Add _test_solve_trac_18572 (autogenerated)
​af1e885	_test_solve_trac_18572: Replace float integers by integers to make test suitable for PPL backend

[mkoeppe]

Rebased on top of #20323 branch on top of 7.2.beta4

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​6d01dc8	Revert "GenericBackend: Remove failing _test methods from this ticket to make the patchbot and its friends happy"
​850b817	Add _test_solve_trac_18572 (autogenerated)
​a5a1c60	_test_solve_trac_18572: Replace float integers by integers to make test suitable for PPL backend

[mkoeppe]

Rebased on top of 7.2.beta5. Dropped "Test backend.copy() rather than copy(backend)".

[dimpase]

How do you do test autogeneration (mentioned in 850b817) ?

[mkoeppe]

The test method added in this commit is the raw output from #20376 (LoggingBackend) when run on the testcase of #18572.

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​cc0d326	Revert "GenericBackend: Remove failing _test methods from this ticket to make the patchbot and its friends happy"
​6cd0b4a	Add _test_solve_trac_18572 (autogenerated)
​492534d	_test_solve_trac_18572: Replace float integers by integers to make test suitable for PPL backend
​658972c	Fix doctests when Gurobi is installed
​cfaf157	Instead of running MixedIntegerLinearProgram doctests with the default solver, use GLPK
​bb7f5de	Merge branch 't/20328/tests_related_to_cplex___gurobi' into t/20424/backend_testsuite_failing_tests

[mkoeppe]

rebased on 7.2.beta6

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. Last 10 new commits:

​f0ead34	CPLEXBackend: Use CPXgetstat to properly detect unboundedness
​4aeaf9b	GurobiBackend.add_col: Implement
​a65f66b	GenericBackend._test_add_col: New
​51c2116	GurobiBackend.add_variable: Support coefficients keyword
​c2eb25d	GurobiBackend: Fix GRB_INFINITY confusion
​6adf3d9	CVXOPTBackend: Don't test _test_solve because of #18572
​def61de	Add _test_solve_trac_18572 (autogenerated)
​9f287a3	_test_solve_trac_18572: Replace float integers by integers to make test suitable for PPL backend
​b60d790	CVXOPTBackend: Disable _test_solve_trac_18572 because of #18572
​07c9c5d	GLPKExactBackend: Adjust output

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​1ce4eb6

CoinBackend.add_col: Use all coefficients

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. Last 10 new commits:

​e43bdc9	GurobiBackend.add_col: Implement
​f42bd1c	GenericBackend._test_add_col: New
​d4eccf6	GurobiBackend.add_variable: Support coefficients keyword
​e9eb094	GurobiBackend: Fix GRB_INFINITY confusion
​bc739f3	CVXOPTBackend: Don't test _test_solve because of #18572
​9639a1f	Add _test_solve_trac_18572 (autogenerated)
​c2bb379	_test_solve_trac_18572: Replace float integers by integers to make test suitable for PPL backend
​0d75d6e	CVXOPTBackend: Disable _test_solve_trac_18572 because of #18572
​b2b3031	GLPKExactBackend: Adjust output
​97c4542	CoinBackend.add_col: Use all coefficients

[mkoeppe]

rebased on 7.3.beta5

[dimpase]

looks good to me

[jdemeyer]

Replying to git:

​d4eccf6

GurobiBackend.add_variable: Support coefficients keyword

Are there any plans to support this for other backends? I noticed that it's not even documented in add_variable.__doc__ for the Gurobi backend.

The interface between backends should be consistent, so even just raise NotImplementedError("the foo backend does not support the 'coefficients' argument") in other backends would be good to have. What do you think?

[dimpase]

IMHO different backends might have different features, which might be impossible to have for each backend.

Only if there are multiple backend supporting this, we can think of adding it to the generic backend, with the default implementation as you propose.

[mkoeppe]

Replying to jdemeyer:

Replying to git:

​d4eccf6

GurobiBackend.add_variable: Support coefficients keyword

Are there any plans to support this for other backends? I noticed that it's not even documented in add_variable.__doc__ for the Gurobi backend.

Yes, there is a plan, see #20324.