Update giant component example (#4267)

* Update comment section about dependencies.

Use try except.

* Switch from plt to fig,ax approach for subplots

* De-emphasize non-connected nodes in visualization

* Make nodes more visible and refactor code

* Seed example and remove layout try/except

Co-authored-by: Jarrod Millman <jarrod.millman@gmail.com>

1 files changed, 21 insertions, 17 deletions

diff --git a/examples/drawing/plot_giant_component.py b/examples/drawing/plot_giant_component.py
index ce7101e4..e8fca7ef 100644
--- a/examples/drawing/plot_giant_component.py
+++ b/examples/drawing/plot_giant_component.py
@@ -13,43 +13,47 @@ import matplotlib.pyplot as plt
 import networkx as nx
 
 # This example needs Graphviz and either PyGraphviz or pydot.
-# from networkx.drawing.nx_pydot import graphviz_layout as layout
 from networkx.drawing.nx_agraph import graphviz_layout as layout
 
-# If you don't have pygraphviz or pydot, you can do this
-# layout = nx.spring_layout
-
 
 n = 150  # 150 nodes
 # p value at which giant component (of size log(n) nodes) is expected
 p_giant = 1.0 / (n - 1)
 # p value at which graph is expected to become completely connected
-p_conn = math.log(n) / float(n)
+p_conn = math.log(n) / n
 
 # the following range of p values should be close to the threshold
 pvals = [0.003, 0.006, 0.008, 0.015]
 
-region = 220  # for pylab 2x2 subplot layout
-plt.subplots_adjust(left=0, right=1, bottom=0, top=0.95, wspace=0.01, hspace=0.01)
-for p in pvals:
-    G = nx.binomial_graph(n, p)
-    pos = layout(G)
-    region += 1
-    plt.subplot(region)
-    plt.title(f"p = {p:.3f}")
-    nx.draw(G, pos, with_labels=False, node_size=10)
+fig, axes = plt.subplots(2, 2)
+for p, ax, seed in zip(pvals, axes.ravel(), range(len(pvals))):
+    #### generate graph ####
+    G = nx.binomial_graph(n, p, seed=seed)
+    # identify connected/disconnected nodes
+    connected = [n for n, d in G.degree() if d > 0]
+    disconnected = list(set(G.nodes()) - set(connected))
     # identify largest connected component
     Gcc = sorted(nx.connected_components(G), key=len, reverse=True)
     G0 = G.subgraph(Gcc[0])
-    nx.draw_networkx_edges(G0, pos, edge_color="r", width=6.0)
-    # show other connected components
+    #### draw graph ####
+    pos = layout(G)
+    ax.set_title(f"p = {p:.3f}")
+    # draw largest connected component
+    options = {"ax": ax, "edge_color": "tab:red"}
+    nx.draw_networkx_edges(G0, pos, width=6.0, **options)
+    # draw other connected components
     for Gi in Gcc[1:]:
         if len(Gi) > 1:
             nx.draw_networkx_edges(
                 G.subgraph(Gi),
                 pos,
-                edge_color="r",
                 alpha=0.3,
                 width=5.0,
+                **options,
             )
+    # draw connected/disconnected nodes
+    options = {"ax": ax, "node_size": 30, "edgecolors": "white"}
+    nx.draw(G, pos, nodelist=connected, **options)
+    nx.draw(G, pos, nodelist=disconnected, alpha=0.25, **options)
+fig.tight_layout()
 plt.show()