Google OR-tools Pickups and deliverys Multiple Visits of same node - or-tools

Question

I'm currently using C# and the Google-Or-Tools to solve an VRP problem
Problem Statement:
I have one Depot node 0 and 3 location nodes (1,2) (1',3) (4,5).
Location 1 and 1' is same location (2 order).
VehicleCapacities: 10
At location 1 I need to pickup 10 units
At location 2 I need to dropoff 10 units
At location 1' I need to pickup 5 units
At location 3 I need to dropoff 5 units
Run the program, it displays the following routes
Route 1: 0 Load(0) -> 1 Load(10) -> 2 Load(0) -> 1' Load(5) -> 3 Load(0) -> 4 Load(10) -> 5 Load(0)
https://ibb.co/3sYxQYH (Sorry, I can't upload image)
My question is how to use or-tools to implement a solver that:
Allows each location only visit one time
example
Route 1: 0 Load(0) -> 1 Load(10) -> 2 Load(0) -> 4 Load(10) -> 5 Load(0)
Route 2: 0 Load(0) -> 1' Load(5) -> 3 Load(0)
Location can visits multiple when it's continuous (1 need to pickup 5 unit, 1' need to pickup 5 units)
example: 0 Load(0) -> 1 Load(5) -> 1' Load(10) -> 2 Load(5) -> 3 Load(0) -> 4 Load(10) -> 5 Load(0)

Answer 1

To limit the route to visit only one node among a list (here [1, 1']).
I would:
Create a "location_token" RoutingDimension with:
Force all slack to 0
Set capacity vehicle to at least 1
Force start cumul to zero
increase by one when visiting 1, 1'
note: use an unary callback like in the capacity sample (https://developers.google.com/optimization/routing/cvrp#demand)
token_transit_callback(from_index):
from_node = manager.IndexToNode(from_index)
# return one upon visiting 1 or 1'
if from_node in (one_node, one_prime_node):
return 1
return 0
token_transit_callback_index = routing.RegisterUnaryTransitCallback(
token_transit_callback)
routing.AddDimension(
token_transit_callback_index,
0, # no slack
1, # vehicle capacity
True, # force start cumul to zero
'location_token')
Add a constraint to visit 1 or 1' you need the "location_one_token" dimension to be zero (i.e. you didn't already visit some nodes in the list).
node_list = [one_node, one_prime_node] # 1, 1'
location_token_dim = routing.GetDimensionOrDie('location_token')
for node in node_list:
index = manager.NodeToIndex(node)
routing.Solver().Add(location_token_dim.CumulVar(index) < 1)
If you want to allow 1 -> 1' or 1' -> 1, Then I would use a regular callback with the usual two parameters from_index and to_index.
The trick will be to not increase the token count if for transit(1, 1') and transit(1, 1`)
something like this:
token_transit_callback(from_index, to_index):
from_node = manager.IndexToNode(from_index)
to_node = manager.IndexToNode(to_index)
out = 0
# return one upon visiting 1 or 1'
if from_node in (one_node, one_prime_node):
out = 1
# except if next node is 1 or 1'
if to_node in (one_node, one_prime_node):
out = 0
return out