为什么Gurobi的探索节点数量显示为零？

Question

我已经实现在Gurobi的数学模型，我想知道为什么探索节点的数量为0 跟踪文件看起来是这样的：

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 

它说，最佳的解决方案是发现，在这一点上我同意，但这是正常的情况？

我必须说，我的数学模型的输入大小很小，所以它有意义吗？

谢谢。

Answer 1

Gurobi以启发式的方式在根节点中解决了您的模型，发现了一个可行的解决方案，其目标值为3900.6420000。这个解决方案在所需的MIP差距内，所以解决过程在Gurobi开始真正建立分支定界树之前就已经完成了。根节点被认为是节点零。这是它最终说它没有探索任何节点。