python: Add vrp_nodes_indices

makefiles/Makefile.python.mk

@@ -605,6 +605,7 @@ test_python_constraint_solver_samples: \
  rpy_vrp_drop_nodes \
  rpy_vrp_global_span \
  rpy_vrp_initial_routes \
+ rpy_vrp_nodes_indices \
  rpy_vrp_pickup_delivery \
  rpy_vrp_pickup_delivery_fifo \
  rpy_vrp_pickup_delivery_lifo \

ortools/constraint_solver/samples/vrp_nodes_indices.py

@@ -0,0 +1,100 @@
+#!/usr/bin/env python3
+# Copyright 2010-2021 Google LLC
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# [START program]
+"""Sample to better understand Node/Index relation.
+
+This script generate few markdown tables to better understand
+the relation between nodes and indices.
+
+Things to notice:
+* Since we have two duplicates (node 5 and node 4) solver need 2 extra indices to have an unique index for each vehicle start/stop and locations.
+* Solver needs to "create" an index for a vehicle 1 start since solver need an unique start index per vehicle.
+* All end nodes are moved to the end of the index list aka [15, 16, 17, 18].
+* routing.Size() return the number of node which are not end nodes (here 15 aka [0-14])
+note: using the two properties above, we know that any index in range(routing.Size()) is not a vehicle end node.
+
+* Since end nodes are moved to the end, their respective "empty" node index are
+reused so all locations indices are "shifted"
+e.g. node 9 is mapped to index 6
+* Same for start nodes which are moved to "empty" space
+e.g. start node 7 mapped to index 4
+
+Takeaway:
+* Allways use routing.Start(), routing.End(), manager.IndexToNode() or manager.NodeToIndex().
+* Location node is not necessarily equal to its index.
+* To loop through ALL indices use manager.GetNumberOfIndices() (Python) or manager::num_indices() (C++)
+"""
+
+from ortools.constraint_solver import routing_enums_pb2
+from ortools.constraint_solver import pywrapcp
+
+
+def main():
+    """Entry point of the program."""
+    locations = 17
+    starts = [5, 5, 7, 8]
+    ends = [1, 2, 4, 4]
+    vehicles = len(starts)
+    assert len(starts) == len(ends)
+
+    manager = pywrapcp.RoutingIndexManager(locations, vehicles, starts, ends)
+    routing = pywrapcp.RoutingModel(manager)
+
+    print('Starts/Ends:')
+    header = '| |'
+    separator = '|---|'
+    v_starts = '| start |'
+    v_ends = '| end |'
+    for v in range(manager.GetNumberOfVehicles()):
+        header += f' vehicle {v} |'
+        separator += '---|'
+        v_starts += f' {starts[v]} |'
+        v_ends += f' {ends[v]} |'
+    print(header)
+    print(separator)
+    print(v_starts)
+    print(v_ends)
+
+    print('\nNodes:')
+    print('| locations | manager.GetNumberOfNodes | manager.GetNumberOfIndices | routing.nodes | routing.Size |')
+    print('|---|---|---|---|---|')
+    print(f'| {locations} | {manager.GetNumberOfNodes()} | {manager.GetNumberOfIndices()} | {routing.nodes()} | {routing.Size()} |')
+
+    print('\nLocations:')
+    print('| node | index | routing.IsStart | routing.IsEnd |')
+    print('|---|---|---|---|')
+    for node in range(manager.GetNumberOfNodes()):
+        if node in starts or node in ends:
+            continue
+        index = manager.NodeToIndex(node)
+        print(
+            f'| {node} | {index} | {routing.IsStart(index)} | {routing.IsEnd(index)} |'
+        )
+
+    print('\nStart/End:')
+    print('| vehicle | Start/end | node | index | routing.IsStart | routing.IsEnd |')
+    print('|---|---|---|---|---|---|')
+    for v in range(manager.GetNumberOfVehicles()):
+        start_index = routing.Start(v)
+        start_node = manager.IndexToNode(start_index)
+        print(f'| {v} | start | {start_node} | {start_index} | {routing.IsStart(start_index)} | {routing.IsEnd(start_index)} |')
+    for v in range(manager.GetNumberOfVehicles()):
+        end_index = routing.End(v)
+        end_node = manager.IndexToNode(end_index)
+        print(f'| {v} | end  | {end_node} | {end_index} | {routing.IsStart(end_index)} | {routing.IsEnd(end_index)} |')
+
+
+if __name__ == '__main__':
+    main()
+# [END program]