graph/network: add diameter example for Eccentricity

graph/network/distance_example_test.go

@@ -0,0 +1,34 @@
+// Copyright ©2025 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package network_test
+
+import (
+	"fmt"
+
+	"gonum.org/v1/gonum/graph/network"
+	"gonum.org/v1/gonum/graph/path"
+	"gonum.org/v1/gonum/graph/simple"
+)
+
+func ExampleEccentricity_diameter() {
+	// Build a simple graph: n1--n2--n3.
+	var n1, n2, n3 simple.Node = 1, 2, 3
+	g := simple.NewUndirectedGraph()
+	g.SetEdge(simple.Edge{F: n1, T: n2})
+	g.SetEdge(simple.Edge{F: n2, T: n3})
+
+	// Find shortest paths and calculate eccentricity values.
+	paths := path.DijkstraAllPaths(g)
+	e := network.Eccentricity(g, paths)
+
+	// Compute the graph's diameter from the eccentricities.
+	var diameter float64
+	for _, d := range e {
+		diameter = max(d, diameter)
+	}
+	fmt.Printf("diameter = %v", diameter)
+
+	// Output: diameter = 2
+}