Changing coefficients in the constraint

Answered

Nazmi Sener

August 15, 2021 13:44

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Dear all,

I try to change coefficients of decision variable z for each scenario s. However z is used with two different coefficients. The constraint is given below. How can I do it?

Thanks in advance,

Have a nice day,

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:50 Edited

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  Jaromił Najman

  • Gurobi Staff

  August 16, 2021 07:50 Edited

  Hi Nazmi,

  Gurobi reformulates the model such that every variable has exactly 1 coefficient. This means that the sum of your \(z\) variables actually looks like this

  \[\sum_{j \in \mathcal{N}, j \neq k} \left (d_{ij}(s)z_{jk}(s)\right) + (d_{ik}(s) - O_i(s))z_{kk}(s)\]

  Thus, you have to change the coefficient given by \((d_{ik}(s) - O_i(s))\).

  Best regards,
  Jaromił

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  Nazmi Sener

  August 16, 2021 09:31

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  Hi Jaromil,

  Thank you for your quick response. i is not equal to k also. I will try to rewrite this constraint. Another question: How can I change coefficient of any parameter in python? I cannot fully understand.

  Thank you,

  Kind regards,

   

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  Jaromił Najman

  • Gurobi Staff

  August 16, 2021 11:27

  Hi Nazmi,

  You can use the chgCoeff function. To use it, you have to provide the constraint, variable, and the new coefficient value.

  Best regards,
  Jaromił

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