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"""
.. _tutorials-maxflow:
============
Maximum Flow
============
This example shows how to construct a max flow on a directed graph with edge capacities using :meth:`igraph.Graph.maxflow`.
"""
import igraph as ig
import matplotlib.pyplot as plt
# %%
# First, we generate a graph and assign a "capacity" to each edge:
g = ig.Graph(6, [(3, 2), (3, 4), (2, 1), (4, 1), (4, 5), (1, 0), (5, 0)], directed=True)
g.es["capacity"] = [7, 8, 1, 2, 3, 4, 5]
# %%
# To find the max flow, we can simply run:
flow = g.maxflow(3, 0, capacity=g.es["capacity"])
print("Max flow:", flow.value)
print("Edge assignments:", flow.flow)
# Output:
# Max flow: 6.0
# Edge assignments [1.0, 5.0, 1.0, 2.0, 3.0, 3.0, 3.0]
# %%
# Finally, we can plot the directed graph to look at the situation:
fig, ax = plt.subplots()
ig.plot(
g,
target=ax,
layout="circle",
vertex_label=range(g.vcount()),
vertex_color="lightblue",
)
plt.show()
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