CODEWITHSUNDEEP
optimizationor-tools
mommomonthewind
mommomonthewind

Reputation: 4640

Google-OR: how to set the minimum constraint with dimension

According to Google-OR doc: https://developers.google.com/optimization/reference/constraint_solver/routing/RoutingModel#AddDimension the add dimension allows only to set the upper bound of something.

I am trying to set the lower bound of the distance of a vehicle on a route in the Pickup and Delivery Problem (https://developers.google.com/optimization/routing/pickup_delivery). I tried:

def negative_distance_callback (from_index, to_index):
    """
    return the negative distance, use for minimization
    """
    return -1 * distance_callback(from_index, to_index)
transit_neg_callback_index = routing.RegisterTransitCallback(negative_distance_callback)

dimension_name = 'Negative_Distance'
routing.AddDimension(
    transit_neg_callback_index,
    0,  # no slack
    -1000,  # vehicle minimum travel distance
    True,  # start cumul to zero
    dimension_name)
negative_distance_dimension = routing.GetDimensionOrDie(dimension_name)
negative_distance_dimension.SetGlobalSpanCostCoefficient(100)

The idea is to create a negative distance callback and try to maximize that.

However, I met the error: Check failed: min_capacity >= 0 (-1000 vs. 0)

How could I set the minimum constraint for the PDP problem with Google-OR?

Many thanks

Upvotes: 0

Views: 426

Answers (1)

Laurent Perron
Laurent Perron

Reputation: 11014

Search the mailing list. This is a frequent question.

In short:

  • setting a hard limit is a bad idea as it quickly lead to infeasible problem.
  • a better solution is to use a soft lower bound on the cumul variable at the end of the route of each vehicle.

Upvotes: 3

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