py3: fix round issue with cplex and gurobi

[dcoudert]

When cplex is installed, the following occur

sage: g = graphs.PetersenGraph()
sage: g.vertex_connectivity()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-8e3aa0688fc2> in <module>()
----> 1 g.vertex_connectivity()

/Users/dcoudert/sage3/sage/local/lib/python3.7/site-packages/sage/graphs/connectivity.pyx in sage.graphs.connectivity.vertex_connectivity (build/cythonized/sage/graphs/connectivity.c:17319)()
   1451 
   1452     if value_only:
-> 1453         return Integer(round(p.solve(objective_only=True, log=verbose)))
   1454 
   1455     val = Integer(round(p.solve(log=verbose)))

TypeError: type sage.rings.real_double.RealDoubleElement doesn't define __round__ method

CC: @seblabbe

Component: numerical

Keywords: thursdaysbdx

Author: David Coudert

Branch/Commit: 57b4539

Reviewer: Sébastien Labbé

Issue created by migration from https://trac.sagemath.org/ticket/27773

[dcoudert]

New commits:

57b4539

trac #27773: issue with cplex

[dcoudert]

Branch: public/numerical/27773_cplex

[dcoudert]

Commit: 57b4539

[dcoudert]

comment:2

I tried to put a doctest with sage: round(p.solve()), but it's not using the same round...

[seblabbe]

Reviewer: Sébastien Labbé

[seblabbe]

Changed keywords from none to thursdaysbdx

[seblabbe]

comment:5

As a remark, I do not have cplex installed, but I confirm it works with Gurobi.

[vbraun]

Changed branch from public/numerical/27773_cplex to 57b4539