87 lines
2.9 KiB
Python
87 lines
2.9 KiB
Python
# Copyright 2010-2014 Google
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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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"""MaxFlow and MinCostFlow examples."""
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from ortools.graph import pywrapgraph
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def MaxFlow():
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"""MaxFlow simple interface example."""
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print 'MaxFlow on a simple network.'
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tails = [0, 0, 0, 0, 1, 2, 3, 3, 4]
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heads = [1, 2, 3, 4, 3, 4, 4, 5, 5]
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capacities = [5, 8, 5, 3, 4, 5, 6, 6, 4]
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expected_total_flow = 10
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max_flow = pywrapgraph.SimpleMaxFlow()
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for i in range(0, len(tails)):
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max_flow.AddArcWithCapacity(tails[i], heads[i], capacities[i])
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if max_flow.Solve(0, 5) == max_flow.OPTIMAL:
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print 'Total flow', max_flow.OptimalFlow(), '/', expected_total_flow
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for i in range(max_flow.NumArcs()):
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print 'From source %d to target %d: %d / %d' % (
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max_flow.Tail(i),
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max_flow.Head(i),
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max_flow.Flow(i),
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max_flow.Capacity(i))
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print 'Source side min-cut:', max_flow.GetSourceSideMinCut()
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print 'Sink side min-cut:', max_flow.GetSinkSideMinCut()
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else:
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print 'There was an issue with the max flow input.'
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def MinCostFlow():
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"""MinCostFlow simple interface example.
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Note that this example is actually a linear sum assignment example and will
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be more efficiently solved with the pywrapgraph.LinearSumAssignement class.
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"""
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print 'MinCostFlow on 4x4 matrix.'
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num_sources = 4
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num_targets = 4
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costs = [[90, 75, 75, 80],
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[35, 85, 55, 65],
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[125, 95, 90, 105],
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[45, 110, 95, 115]]
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expected_cost = 275
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min_cost_flow = pywrapgraph.SimpleMinCostFlow()
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for source in range(0, num_sources):
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for target in range(0, num_targets):
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min_cost_flow.AddArcWithCapacityAndUnitCost(
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source, num_sources + target, 1, costs[source][target])
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for node in range(0, num_sources):
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min_cost_flow.SetNodeSupply(node, 1)
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min_cost_flow.SetNodeSupply(num_sources + node, -1)
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status = min_cost_flow.Solve()
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if status == min_cost_flow.OPTIMAL:
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print 'Total flow', min_cost_flow.OptimalCost(), '/', expected_cost
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for i in range(0, min_cost_flow.NumArcs()):
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if min_cost_flow.Flow(i) > 0:
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print 'From source %d to target %d: cost %d' % (
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min_cost_flow.Tail(i),
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min_cost_flow.Head(i) - num_sources,
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min_cost_flow.UnitCost(i))
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else:
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print 'There was an issue with the min cost flow input.'
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def main(unused_argv):
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MaxFlow()
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MinCostFlow()
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if __name__ == '__main__':
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main()
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