Can MIPSOL happens in the PRESOLVE?

Answered

haonan zhong

June 29, 2026 15:57

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I'm adding lazy cut in the callbacks. I realize that a feasible solution is found (Not optimal), but the number of node reported by Gurobi is only one. Is it because the lazy cut is added in the PRESOLVE and the feasible solution is found in the PRESOLVE?

Related to

• Lazy Constraints

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  Riley Clement

  • Gurobi Staff

  June 30, 2026 01:32

  Hi Haonan,

  Yes, feasible solutions can be found during presolve as we have some simple heuristics which run in parallel threads during presolve.

  - Riley

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  haonan zhong

  June 30, 2026 15:36

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  Hi Riley, 

  Thanks for your response! I just want to mention that I'm implementing this code in a lazy-fashion using lazy constraints. I'm not giving the model the lazy constraints that are removed before calling the solver. How does the solver find a feasible solution and verifies feasibility in PRESOLVE without having the lazy constraints?

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  Riley Clement

  • Gurobi Staff

  June 30, 2026 22:34

  Hi Haonan,

  When Gurobi finds a solution it will call your callback method using a “MIPSOL” argument for the where parameter, which gives you a chance to cut the solution off with a lazy constraint.  It doesn't matter when the solution is found, the callback is activated regardless.

  - Riley

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