问题描述
我正在尝试使用 OR-Tools 的路由求解器来解决多行程电容 VRP。我需要的是
所以车辆应该从每个节点取货，直到容量填满为止。然后去“卸货地点”，卸掉他们所有的重量，不断地收集节点的需求，直到达到时间限制或所有的货物都被收集起来。然后返回仓库。
CVRP Reload Example 看起来很近，但在我的情况下，在路线的尽头，车辆应该在仓库之前到达卸货地点。换句话说，车辆不能带负载去车站（起点、终点）。
示例：
0: Depot
1: Unloading Location
2,3,4,5,6,7: Nodes to pick up demand
0 > 2 > 3 > 4 > 1 (unload) > 5 > 6 > 7 > 1 (unload) > 0
0 > 2 > 3 > 4 > 1 (unload) > 5 > 6 > 7 > 0 This is the result cvrp_reload returns.
我对 or-tools 相当陌生，并试图弄清楚。如果您有任何想法，可以帮助我吗？
- 我使用的是 Python 和 or-tools v8.2
- 这是来自github的交叉帖子。
我认为，可以通过使用 count_dimension 在最后一点（在仓库之前卸载）之前实现前面的约束，但我不知道如何实现。
解决方法
只需添加
# Vehicles must be empty upon arrival
capacity_dimension = routing.GetDimensionOrDie("Capacity")
for v in range(manager.GetNumberOfVehicles()):
print(f"vehicle {v}")
end = routing.End(v)
#routing.solver().Add(capacity_dimension.CumulVar(end) == 0) # see comment below
capacity_dimension.SetCumulVarSoftUpperBound(end,100_000)
可能的输出：
./2442_unload.py
...
I0417 23:53:02.181640 17437 search.cc:260] Solution #317 (372696,objective maximum = 4838552,time = 2969 ms,branches = 3223,failures = 940,depth = 33,MakeInactiveOperator,neighbors = 265820,filtered neighbors = 317,accepted neighbors = 317,memory used = 14.93 MB,limit = 99%)
I0417 23:53:20.290527 17437 search.cc:260] Solution #318 (469816,objective minimum = 372696,time = 2987 ms,branches = 3239,failures = 945,neighbors = 267395,filtered neighbors = 318,accepted neighbors = 318,limit = 99%)
I0417 23:53:21.045410 17437 search.cc:260] Solution #319 (469816,time = 2988 ms,branches = 3247,failures = 947,MakeActiveOperator,neighbors = 267415,filtered neighbors = 319,accepted neighbors = 319,limit = 99%)
I0417 23:53:22.304931 17437 search.cc:260] Solution #320 (372696,time = 2989 ms,branches = 3253,failures = 949,neighbors = 267464,filtered neighbors = 320,accepted neighbors = 320,limit = 99%)
I0417 23:53:30.987548 17437 search.cc:260] Finished search tree (time = 2998 ms,branches = 3259,failures = 982,neighbors = 268318,accepted neigbors = 320,memory used = 14.93 MB)
I0417 23:53:31.046630 17437 search.cc:260] End search (time = 2998 ms,speed = 1087 branches/s)
Objective: 372696
dropped orders: [25]
dropped reload stations: [3,5]
Route for vehicle 0:
0 Load(0) Time(0,0) -> 20 Load(0) Time(75,506) -> 12 Load(3) Time(94,525) -> 14 Load(6) Time(119,550) -> 13 Load(10) Time(140,700) -> 8 Load(13) Time(159,1000) -> 0 Load(0) Time(237,1500)
Distance of the route: 2624m
Load of the route: 0
Time of the route: 237min
Route for vehicle 1:
1 Load(0) Time(0,0) -> 19 Load(0) Time(2,182) -> 24 Load(3) Time(20,200) -> 26 Load(7) Time(42,400) -> 4 Load(15) Time(89,770) -> 7 Load(15) Time(92,773) -> 11 Load(0) Time(169,850) -> 17 Load(3) Time(188,959) -> 10 Load(11) Time(229,1000) -> 1 Load(0) Time(307,1500)
Distance of the route: 2648m
Load of the route: 0
Time of the route: 307min
Route for vehicle 2:
2 Load(0) Time(0,0) -> 23 Load(0) Time(15,63) -> 22 Load(4) Time(37,85) -> 21 Load(7) Time(85,101) -> 9 Load(10) Time(104,120) -> 18 Load(0) Time(184,200) -> 16 Load(8) Time(226,600) -> 15 Load(12) Time(248,800) -> 6 Load(15) Time(268,1000) -> 2 Load(0) Time(346,1500)
Distance of the route: 2624m
Load of the route: 0
Time of the route: 346min
Total Distance of all routes: 7896m
Total Load of all routes: 0
Total Time of all routes: 890min
注意：我使用软约束，否则求解器更喜欢删除所有节点，并且永远不会设法逃离此解决方案搜索空间点。