I have implemented a mathematical model in Gurobi and I was wondering why the number of explored nodes is 0. The trace file looks like this :
Optimize a model with 276 rows, 492 columns and 1434 nonzeros
Model has 324 general constraints
Variable types: 0 continuous, 492 integer (492 binary)
Coefficient statistics:
Matrix range [1e+00, 5e+02]
Objective range [2e-02, 8e-02]
Bounds range [1e+00, 1e+00]
RHS range [1e+00, 8e+03]
Found heuristic solution: objective 3900
Presolve removed 335 rows and 570 columns
Presolve time: 0.01s
Presolved: 265 rows, 246 columns, 1302 nonzeros
Variable types: 0 continuous, 246 integer (246 binary)
Root relaxation: objective 3.900689e+03, 43 iterations, 0.00 seconds
Nodes | Current Node | Objective Bounds | Work
Expl Unexpl | Obj Depth IntInf | Incumbent BestBd Gap | It/Node Time
0 0 3900.68909 0 9 3900.00000 3900.68909 0.02% - 0s
H 0 0 3900.6420000 3900.68909 0.00% - 0s
Explored 0 nodes (104 simplex iterations) in 0.03 seconds
Thread count was 8 (of 8 available processors)
Solution count 2: 3900.64 3900
Pool objective bound 3900.69
Optimal solution found (tolerance 1.00e-04)
Best objective 3.900642000000e+03, best bound 3.900689090909e+03, gap 0.0012%
Optimal objective: 3900.64
It says that the optimal solution was find, at this point I agree but is it normal scenario ?
I have to say that the size of input to my mathematical model is small, so does it makes sense ?
Thanks.
Gurobi solved your model in the root node as a heuristic found a feasible solution with objective value of 3900.6420000. This solution is within the desired MIP gap, so the solving process is finished before Gurobi started to really build the branch-and-bound tree. The root node is considered as node zero. This is way it says in the end that it did not explore any nodes.