Network flow and Truck capacity

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Timothy McCormack

2021年11月12日 12:47

Hi,

 

We have built a multi-objective supply chain model in Gurobi. The current model executes.

However, we wish to get a more accurate assessment of the cost of shipping. We want to round up partly filled trucks to the next whole number. i.e 2.3 to 3.  Here is the code:

cost = ((gp.quicksum((flow[p,a[0],a[1]]/TruckCapacity[a]) *FixedCost[a] for p in Products for a in arcs )

We have tried to include math.ceil, but it says it is not a Gurobi LinExpr.

Would we be able to implement a constraint that forces Gurobi to do it?

If anybody can help, it would be greatly appreciated?

Tim

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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 02:44 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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  Jaromił Najman

  • Gurobi Staff

  2021年11月15日 09:56

  Hi Tim,

  There is no built in rounding function for mathematical programming. You can however, introduce auxiliary integer variables to force the cost of shipping to attain integer values, i.e., add constraints

  cost_of_shipping = auxiliary_integer_variable

  If your current model does not allow for integer value of \(\texttt{cost_of_shipping}\) you could introduce auxiliary continuous variables \(x \in [0,0.999]\) to represent the offset to the next integer value. Rounding up could then be modeled as

  cost_of_shipping + x = auxiliary_integer_variable

  In your example, when cost of shipping equals \(2.3\), \(x\) would be \(0.7\) and the auxiliary integer vairable then \(3\).

  Best regards,
  Jaromił

  Best regards,
  Jaromił

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