Positive GAP interpretation when an optimal solution is found

Carlos Monardes

• June 09, 2020 22:32

Hi everyone:
I solved a BIP problem given 1800 seconds as a time limit. Gurobi only used less than 3 seconds to solve the model, but the Gap reported was 100%. How can I interpret the gap value different from zero, when it is supposed that the optimal solution was reached? Here is the log:

Changed value of parameter TimeLimit to 1800.0
Prev: 1e+100 Min: 0.0 Max: 1e+100 Default: 1e+100
Changed value of parameter lazyConstraints to 1
Prev: 0 Min: 0 Max: 1 Default: 0
Optimize a model with 15 rows, 770 columns and 1030 nonzeros
Variable types: 0 continuous, 770 integer (770 binary)
Coefficient statistics:
Matrix range [1e+00, 1e+00]
Objective range [1e+00, 1e+00]
Bounds range [1e+00, 1e+00]
RHS range [1e+00, 1e+00]
Presolve time: 0.00s
Presolved: 15 rows, 770 columns, 1030 nonzeros
Variable types: 0 continuous, 770 integer (770 binary)

Root relaxation: objective 0.000000e+00, 15 iterations, 0.00 seconds

Nodes | Current Node | Objective Bounds | Work
Expl Unexpl | Obj Depth IntInf | Incumbent BestBd Gap | It/Node Time

0 0 0.00000 0 6 - 0.00000 - - 1s
0 0 0.00000 0 7 - 0.00000 - - 1s
0 0 0.00000 0 6 - 0.00000 - - 2s
H 0 0 1.0000000 0.00000 100% - 2s

Explored 1 nodes (1596 simplex iterations) in 2.39 seconds
Thread count was 8 (of 8 available processors)

Solution count 1: 1

Optimal solution found (tolerance 1.00e-04)
Best objective 1.000000000000e+00, best bound 0.000000000000e+00, gap 100.0000%

Thanks in advance,

0

• 

  Eli Towle

  Gurobi Staff

  • June 17, 2020 21:56

  This behavior was corrected by upgrading from Gurobi 7.5.2 to Gurobi 9.0.2.

  Eli

  0
• 

  Carlos Monardes

  • June 18, 2020 02:49

  

  

  

  Thanks Eli for your help. Best regards,

  0

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