"""
==============
Directed Graph
==============

Draw a graph with directed edges using a colormap and different node sizes.

Edges have different colors and alphas (opacity). Drawn using matplotlib.
"""

import matplotlib as mpl
import matplotlib.pyplot as plt
import networkx as nx

G = nx.generators.directed.random_k_out_graph(10, 3, 0.5)
pos = nx.layout.spring_layout(G)

node_sizes = [3 + 10 * i for i in range(len(G))]
M = G.number_of_edges()
edge_colors = range(2, M + 2)
edge_alphas = [(5 + i) / (M + 4) for i in range(M)]

nodes = nx.draw_networkx_nodes(G, pos, node_size=node_sizes, node_color="blue")
edges = nx.draw_networkx_edges(
    G,
    pos,
    node_size=node_sizes,
    arrowstyle="->",
    arrowsize=10,
    edge_color=edge_colors,
    edge_cmap=plt.cm.Blues,
    width=2,
)
# set alpha value for each edge
for i in range(M):
    edges[i].set_alpha(edge_alphas[i])

pc = mpl.collections.PatchCollection(edges, cmap=plt.cm.Blues)
pc.set_array(edge_colors)
plt.colorbar(pc)

ax = plt.gca()
ax.set_axis_off()
plt.show()