Counting lazy constraints

回答済み

Amirhossein Abbaszadeh

2024年03月29日 19:48

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Hi all, 

I'm trying to apply Benders Decomposition to a problem using callback function in C++.

I understand that whenever Gurobi found a MIP solution (that is where == GRB_CB_MIPSOL), I must get the incumbent solution using getSolution, then solve the subproblem and check if a cut need to be added using addLazy. 

The condition that I check at each iteration is as follows:

if (varVal[varIndex->thetaOmegaIndex[1]] - subProblem.get(GRB_DoubleAttr_ObjVal) > 0)
{
                //So we need to add a cut!
                addLazy(theCutExpr, GRB_GREATER_EQUAL, 0.0);
                cutCounter++;
}

As you can see in the code, I've also defined the global variable cutCounter to count the cuts that are added to model. I know that the Gurobi gives me the numbers of lazy constraints that have been added to the model.  

The problem is that when I check the Gurobi report and compare it with the cutCounter, I get two different values! (Please see the last sentence of the following log file)

Cutting planes:
  Lazy constraints: 97

Explored 1569 nodes (188581 simplex iterations) in 30.06 seconds (38.02 work units)
Thread count was 1 (of 16 available processors)

Solution count 3: 1761 1508 1228

Time limit reached
Best objective 1.761000000000e+03, best bound 6.167127329585e+03, gap 250.2060%

User-callback calls 8903, time in user-callback 10.18 sec

---------------------------------------
cutCounter = 176

Why it's like that? Is it normal? or I'm missing something? 
I can provide more details if required.

Thanks

関連

• Bender's
• Lazy Constraints

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2026年11月13日 01:27

  This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
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  Riley Clement

  • Gurobi Staff

  2024年04月02日 10:27

  Hi Amirhossein,

  This is normal.  Sometimes a lazy constraint that has been added becomes redundant and is removed from the model, lowering the number of lazy constraints reported.

  - Riley

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