All rows and columns removed but still get new incumbent

Answered

liu heng

• November 20, 2023 11:08

I have a current solution 'sol_0' and set v.Start as the current value, then i fix some of the variables and solve the model.

In the presolve stage, all rows and columns are removed but i still get another solution instead of 'sol_0'. Do i do something wrong? If not, why does this happen?

Related to

• Presolve

0

• 

  Michel Soares

  • November 20, 2023 12:22

  

  

  Hello,

  This is a quote from the Start parameter page: "If the Gurobi MIP solver log indicates that your MIP start didn't produce a new incumbent solution, note that there can be multiple explanations. ...  Another, more common possibility is that one of the Gurobi heuristics found a solution that is as good as the solution produced by the MIP start, so the MIP start solution was cut off."

  I believe this is the explanation of what happened in your case.

  The way I see it, providing Gurobi with an initial solution has the main objective of finding a better solution faster. Your model seems to simple enough that this start solution ends up having no effect.

  -1

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