Originally posted by: shchwang

Dear All,

I am using CPLEX to solve the attached problem. But after running it I get:

Tried aggregator 1 time.
MIP Presolve eliminated 55 rows and 0 columns.
Reduced MIP has 189 rows, 99 columns, and 579 nonzeros.
Reduced MIP has 27 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.00 sec. (0.23 ticks)

Root node processing (before b&c):
  Real time             =    0.00 sec. (0.58 ticks)
Parallel b&c, 8 threads:
  Real time             =    0.00 sec. (0.00 ticks)
  Sync time (average)   =    0.00 sec.
  Wait time (average)   =    0.00 sec.
                          ------------
Total (root+branch&cut) =    0.00 sec. (0.58 ticks)


MIP - Integer infeasible.
Current MIP best bound is infinite.
Solution time =    0.00 sec.  Iterations = 0  Nodes = 0
Deterministic time = 0.58 ticks  (171.52 ticks/sec)

So why did this happen? Is CPLEX unable to find a solution that meets my objective and satisfies the constraints?

Any help will be highly appreciated.

Regards.

The presolver in CPLEX determined that there is no feasible solution to your model (no solution satisfies all constraints, regardless of the objective function). in fact, even if you relax the problem to an LP, it is infeasible.

I suggest that you read the problem into the interactive optimizer, run the 'co'  ('conflict') command to identify a conflict, and then run 'di co a' ('display conflict all') to see which constraints and variable bounds are form the conflict (cannot simultaneously be satisfied). Note that there can be more than one conflict set; this identifies one of them.

Paul