70 lines
2.3 KiB
Python
Executable File
70 lines
2.3 KiB
Python
Executable File
#!/usr/bin/env python3
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# Copyright 2010-2022 Google LLC
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# [START program]
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"""From Taha 'Introduction to Operations Research', example 6.4-2."""
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# [START import]
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from ortools.graph.python import max_flow
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import numpy as np
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# [END import]
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def main():
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"""MaxFlow simple interface example."""
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# [START solver]
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# Instantiate a SimpleMaxFlow solver.
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smf = max_flow.SimpleMaxFlow()
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# [END solver]
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# [START data]
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# Define three parallel arrays: start_nodes, end_nodes, and the capacities
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# between each pair. For instance, the arc from node 0 to node 1 has a
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# capacity of 20.
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start_nodes = np.array([0, 0, 0, 1, 1, 2, 2, 3, 3])
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end_nodes = np.array([1, 2, 3, 2, 4, 3, 4, 2, 4])
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capacities = np.array([20, 30, 10, 40, 30, 10, 20, 5, 20])
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# [END data]
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# [START constraints]
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# Add arcs in bulk.
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# note: we could have used add_arc_with_capacity(start, end, capacity)
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smf.add_arcs_with_capacity(start_nodes, end_nodes, capacities)
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# [END constraints]
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# [START solve]
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# Find the maximum flow between node 0 and node 4.
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status = smf.solve(0, 4)
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# [END solve]
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# [START print_solution]
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if status != smf.OPTIMAL:
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print('There was an issue with the max flow input.')
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print(f'Status: {status}')
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exit(1)
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print('Max flow:', smf.optimal_flow())
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print('')
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print(' Arc Flow / Capacity')
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for i in range(smf.num_arcs()):
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print('%1s -> %1s %3s / %3s' %
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(smf.tail(i), smf.head(i), smf.flow(i), smf.capacity(i)))
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print('Source side min-cut:', smf.get_source_side_min_cut())
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print('Sink side min-cut:', smf.get_sink_side_min_cut())
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# [END print_solution]
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if __name__ == '__main__':
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main()
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# [END program]
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