Find the coefficient of a variable in a complex (very large) objective function

Answered

Chris Domnisoru

• February 27, 2021 16:51

Assume the model uses a very complex objective function with lots of variables. Some of those variables may appear more than once in the linear expression.

Given the name of a variable, how can one easily determine the coefficient for it in the expression of the objective function?

Using the LinExpr.getCoeff() does not look promising as it is based on "index i in the expression", and if a variable shows up more than once one would have to process all the variables, and group/sum by variable (names).

In general terms, after an optimization is complete, I simply want to have an easy way to look up the contribution to the objective function from individual variables - to be able to say "ok, this variable contributed a lot or not...", and the problem is challenging because of the shear number of variables. 

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  Jaromił Najman

  Gurobi Staff

  • March 01, 2021 09:19

  Hi Chris,

  Given only the name of a variable, you can get the variable object using the getVarByName function. You can then look up the objective coefficient of a given variable directly via variable attributes.

  Best regards,
  Jaromił

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  Chris Domnisoru

  • March 01, 2021 10:26

  

  

  

  Thank you.

  Indeed, I overlooked the obj attribute and ended up with a more complex solution using the functionality of the linear expression object representing the objective.

  Thank you,

  Chris

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