[Coin-discuss] Cbc 2.2 reports integer-infeasible

[Andrew Makhorin]

> I filed a ticket for Cbc
> https://projects.coin-or.org/Cbc/ticket/58

> The observed behaviour is strange and might be an issue related to the
> MPS standard or Cbc/Cgl.  Cplex 9.1, Cbc 2.2 and Blis report the model
> as integer-infeasible, but GLPK 4.27, Xpress MP, and SCIP report an 
> integer-feasible solution; see the bug report.

In your mps file some integer columns are not listed in the BOUNDS
section. Glpk sets default lower and upper bounds of such columns to 0
and +inf, resp. However, the IBM OSL documentation says:

        "For non-integer variables, the default bounds on columns are
        0 and +inf. For integer variables, the default bounds on columns
        are 0 and 1."

AFAIK, Cbc uses the latter convention that explains why the results
are different.