I have a list of orders, each consists of a disjunction of pickup and a disjunction of delivery nodes (using AddDisjunction with a positive penalty and max cardinality of 1).
- Some of these orders form groups that must be delivered to the same location at the same time by the same vehicle, or not at all.
AddPickupAndDelivery/AddPickupAndDeliverySets cannot be used on the same node/disjunction twice so I cannot merge the delivery disjunctions into one and link all pickup disjunctions to it.
I have tried setting the NextVar of one delivery disjunction to the other delivery disjunction, however the other disjunction was still sometimes reached without the first one (but not vice versa).
I have tried combining the NextVar method with giving penalty for reaching only part of the delivery nodes, in two different ways:
- first by using AddSoftSameVehicleConstraint, however it did not give penalty for unperformed nodes,
- second by creating a new dimension with positive arc values for reaching all disjunctions other than the first one in the NextVar chain, and a negative arc value for reaching the latter, which is the only one that can be reached only if all the rest of the disjunctions were reached. Combined with SetSpanCostCoefficientForAllVehicles and a big cumul var start value at the start nodes, the idea was that reaching part of the nodes would induce a positive span, while reaching all of them would reset the span back to 0.
However at this point the algorithm stopped reaching any nodes, I presume due to the fact that the local search operators do not include a single addition of multiple nodes, and each addition of a single node induces a higher cost. Is there a way of implementing multiple pickups to a single delivery which abides the constraints I have stated while using the python version of or-tools?
