GLPK backend does not detect unboundedness in simplex-only mode

[mkoeppe]

testcase:

sage: p = MixedIntegerLinearProgram(maximization=True, solver = "GLPK")
sage: p.set_objective(p[0])
sage: p.solver_parameter("simplex_or_intopt", "simplex_only")
sage: p.solve()
0.0

CC: @yuan-zhou @nathanncohen @dimpase @johnperry-math @dcoudert

Component: numerical

Author: Matthias Koeppe, Yuan Zhou

Branch/Commit: b8daa1f

Reviewer: Dima Pasechnik, David Coudert

Issue created by migration from https://trac.sagemath.org/ticket/18838

[yuan-zhou]

Description changed:

--- 
+++ 
@@ -1 +1,9 @@
-testcase to be added
+testcase:
+
+```
+sage: p = MixedIntegerLinearProgram(maximization=True, solver = "GLPK")
+sage: p.set_objective(p[0])
+sage: p.solver_parameter("simplex_or_intopt", "simplex_only")
+sage: p.solve()
+0.0
+```

[yuan-zhou]

Branch: u/yzh/glpk_backend_does_not_detect_unboundedness_in_simplex_only_mode

[yuan-zhou]

Commit: 12f5516

[sagetrac-git]

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

dc441f2

More doctests for unboundedness in GLPK backend simplex-only mode.

[sagetrac-git]

Changed commit from 12f5516 to dc441f2

[dimpase]

comment:7

something worries me there:

            status = glp_simplex(self.lp, self.smcp)
            status = glp_get_prim_stat(self.lp)

makes no sense to me...
The ticket proposes to change the 2nd line to

            status = glp_get_status(self.lp)

but still...

[sagetrac-git]

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

597fabf

Include detailed error message for glp_simplex

[sagetrac-git]

Changed commit from dc441f2 to 597fabf

[sagetrac-git]

Changed commit from 597fabf to 54c9bde

[sagetrac-git]

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

54c9bde

Include detailed error message for solve method

[sagetrac-git]

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

4092d35

Distinguish solve_status and solution_status for error status values

[sagetrac-git]

Changed commit from 54c9bde to 4092d35

[sagetrac-git]

Changed commit from 4092d35 to e3f4f87

[sagetrac-git]

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

e3f4f87

Fix bug: solution_status is defined only if solve_status is 0.