How to implement constraint in which nodes are visited optionally?

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Subramanian Ramasamy

2021年04月28日 01:48

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Hello Everyone,

I am a newbie to Gurobi python and I am formulating a CVRP problem. The normal CVRP constraints include satisfying flow constraints, capacity constraints so far. Apart from these constraints, I need to know how to code/formulate a constraint such a way that the nodes can be visited optionally. For example, when a certain constraint is needed to be satisfied, it should visit certain nodes, else, those nodes need not be visited. Can anyone let me know how to model such a constraint in Gurobi python? Looking forward to hearing from you. Thanks.

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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 02:56 編集済み

  This post is more than three 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 why not try our AI Gurobot?.
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  Silke Horn

  • Gurobi Staff

  2021年04月28日 07:52

  Hi,

  Welcome to the Gurobi community!

  Here are a few ideas you could look into:

  • You can model optional constraints (that is, constraints that would be nice but may be violated if necessary) by adding a penalty for violating them to the objective function (instead of adding the constraint itself).
  • If you are looking to implement if-then-constraints, you might want to look at indicator constraints.

  Silke

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  Subramanian Ramasamy

  2021年04月29日 00:16

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  Hi,

  Thank you for your input. I will look into these options. I could understand how indicator constraints would work. I guess I would need indicator constraints for my problem (as I need to implement such a way that a node will be visited only if a variable's value is lesser than some threshold value - hence I guess I need indicator constraints). Though I guess I would need indicator constraints for my problem, I could vaguely understand how does optional constraints that you mentioned in the first bullet point would work. It would be helpful for me if you could provide a short and crisp sample for implementing that optional constraint that you mentioned in the first point. Thank you so much for your help.

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