82 lines
2.5 KiB
Python
82 lines
2.5 KiB
Python
# Copyright 2010-2011 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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"""Min Cost Flow and Max Flow examples."""
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from google.apputils import app
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import gflags
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from graph import pywrapflow
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FLAGS = gflags.FLAGS
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def MinCostFlow():
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"""Min Cost Flow Example."""
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print 'Min Cost Flow 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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graph = pywrapflow.StarGraph(num_sources + num_targets,
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num_sources * num_targets)
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min_cost_flow = pywrapflow.MinCostFlow(graph)
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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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arc = graph.AddArc(source, num_sources + target)
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min_cost_flow.SetArcUnitCost(arc, costs[source][target])
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min_cost_flow.SetArcCapacity(arc, 1)
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for source in range(0, num_sources):
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min_cost_flow.SetNodeSupply(source, 1)
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for target in range(0, num_targets):
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min_cost_flow.SetNodeSupply(num_sources + target, -1)
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total_flow_cost = min_cost_flow.ComputeMinCostFlow()
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print 'total flow', total_flow_cost, '/', expected_cost
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def MaxFeasibleFlow():
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"""Max Flow Example."""
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print 'MaxFeasibleFlow'
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num_nodes = 6
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num_arcs = 9
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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_flows = [4, 4, 2, 0, 4, 4, 0, 6, 4]
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expected_total_flow = 10
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graph = pywrapflow.StarGraph(num_nodes, num_arcs)
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max_flow = pywrapflow.MaxFlow(graph, 0, num_nodes - 1)
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for i in range(0, num_arcs):
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arc = graph.AddArc(tails[i], heads[i])
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max_flow.SetArcCapacity(arc, capacities[i])
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total_flow = max_flow.ComputeMaxFlow()
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print 'total flow', total_flow, '/', expected_total_flow
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for i in range(num_arcs):
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print 'Arc', i, ':', max_flow.Flow(i), '/', expected_flows[i]
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def main(unused_argv):
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MinCostFlow()
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MaxFeasibleFlow()
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if __name__ == '__main__':
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app.run()
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