[Help-glpk] Confused by error messages

[Shreekanth Karvaje]

Hello GLPK users,

I used glpk (4.15) on my linear programming problem and dumped the result
into a text file. At the beginning of the file, it has the following
message:
<quote>
Rows:       274
Columns:    7576 (7350 integer, 7350 binary)
Non-zeros:  1069
Status:     INTEGER OPTIMAL
Objective:  obj = 255.0545959 (MINimum)
</quote>

This gave me an impression that the solver found the optimal solution.
When I check the solution file towards the end, I see this message:
<quote>
Integer feasibility conditions:

INT.PE: max.abs.err. = 5.68e-14 on row 150
        max.rel.err. = 1.42e-14 on row 2
        High quality

INT.PB: max.abs.err. = 4.66e+01 on row 152
        max.rel.err. = 9.79e-01 on row 152
        SOLUTION IS INFEASIBLE
</quote>

Perhaps I am too novice a user to understand these messages. I don't
understand how an integer optimal solution can be found when
the solution is infeasible. Then again, there are two words
INT.PE and INT.PB which I don't understand (and I googled for the meaning
without much success). I would greatly appreciate any help to make me
understand what is going on.

I used glpsol to solve these. I used --intopt with and without
--nopresol, both giving the same result.

Thanks,
Shreekanth