Question

我正在实现B＆C，并使用添加每个惰性约束后加1的计数器。解决之后，我的计算结果与Gurobi作为惰性约束检索的结果之间存在很大差异。造成这种差异的原因是什么？

谢谢。

Changed value of parameter LazyConstraints to 1
   Prev: 0  Min: 0  Max: 1  Default: 0
Optimize a model with 67 rows, 442 columns and 1154 nonzeros
Variable types: 22 continuous, 420 integer (420 binary)
Coefficient statistics:
  Matrix range     [1e+00, 1e+00]
  Objective range  [1e-01, 5e+00]
  Bounds range     [1e+00, 1e+00]
  RHS range        [1e+00, 1e+01]
Presolve removed 8 rows and 42 columns
Presolve time: 0.00s
Presolved: 59 rows, 400 columns, 990 nonzeros
Variable types: 1 continuous, 399 integer (399 binary)

Root relaxation: objective 2.746441e+00, 37 iterations, 0.00 seconds

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

     0     0    4.18093    0   20          -    4.18093      -     -    0s
H    0     0                      21.2155889    4.18093  80.3%     -    0s
     0     0    5.91551    0   31   21.21559    5.91551  72.1%     -    0s
H    0     0                      18.8660609    5.91551  68.6%     -    0s
     0     0    6.35067    0   38   18.86606    6.35067  66.3%     -    0s
H    0     0                      17.9145774    6.35067  64.6%     -    0s
     0     0    6.85254    0   32   17.91458    6.85254  61.7%     -    0s
H    0     0                      17.7591641    6.85254  61.4%     -    0s
     0     0    7.20280    0   50   17.75916    7.20280  59.4%     -    0s
H    0     0                      17.7516768    7.20280  59.4%     -    0s
     0     2    7.91616    0   51   17.75168    7.91616  55.4%     -    0s
*   80    62              30      17.6301180    8.69940  50.7%  10.7    0s
*  169   138              35      16.3820478    9.10423  44.4%   9.9    1s
*  765   486              22      14.6853796    9.65509  34.3%   9.2    2s
* 1315   762              27      14.6428113    9.97011  31.9%   9.4    3s
* 1324   415              14      12.0742408    9.97011  17.4%   9.4    3s
H 1451   459                      11.8261154   10.02607  15.2%   9.7    4s
  1458   463   11.78416   15   58   11.82612   10.02607  15.2%   9.6    5s
* 1567   461              33      11.6541357   10.02607  14.0%  10.6    6s
  4055   906   11.15860   31   36   11.65414   10.69095  8.26%  12.4   10s

Cutting planes:
  Gomory: 4
  Flow cover: 1
  Lazy constraints: 228

Explored 7974 nodes (98957 simplex iterations) in 14.78 seconds
Thread count was 4 (of 4 available processors)

Solution count 10: 11.6541 11.8261 12.0742 ... 17.9146

Optimal solution found (tolerance 1.00e-04)
Best objective 1.165413573861e+01, best bound 1.165413573861e+01, gap 0.0000%


My Lazy constraints counter: 654

Answer 1

优化完成（或停止）后显示的切割平面统计信息仅显示在解决的最终LP松弛中处于活动状态的切割平面的数量。特别是，最后一个节点处于活动状态的惰性约束的数量可能少于在回调中添加的惰性约束的总数。例如，Gurobi可能会在优化过程中添加控制原始延迟约束的内部切割平面，或者使用回调中的延迟约束来导出其他切割，而不是添加原始切割。

Gurobi Lazy削减计数器和自己的计数器之间的区别

1 个答案: