graph: add implicit graph complement type

graph/complement_test.go

@@ -0,0 +1,89 @@
+// Copyright ©2019 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 graph_test
+
+import (
+	"fmt"
+	"testing"
+
+	"golang.org/x/exp/rand"
+
+	"gonum.org/v1/gonum/graph"
+	"gonum.org/v1/gonum/graph/graphs/gen"
+	"gonum.org/v1/gonum/graph/iterator"
+	"gonum.org/v1/gonum/graph/simple"
+)
+
+var complementTests = []struct {
+	g graph.Graph
+}{
+	{g: gnp(100, 0, rand.NewSource(1))},
+	{g: gnp(100, 0.05, rand.NewSource(1))},
+	{g: gnp(100, 0.5, rand.NewSource(1))},
+	{g: gnp(100, 0.95, rand.NewSource(1))},
+	{g: gnp(100, 1, rand.NewSource(1))},
+}
+
+func TestComplement(t *testing.T) {
+	for _, test := range complementTests {
+		n := test.g.Nodes().Len()
+		wantM := n * (n - 1) // Double counting edges, but no self-loops.
+
+		var gotM int
+		iter := test.g.Nodes()
+		for iter.Next() {
+			id := iter.Node().ID()
+			to := test.g.From(id)
+			for to.Next() {
+				gotM++
+			}
+			toC := graph.Complement{test.g}.From(id)
+			for toC.Next() {
+				gotM++
+			}
+		}
+		if gotM != wantM {
+			t.Errorf("unexpected number of edges in sum of input and complement: got:%d want:%d", gotM, wantM)
+		}
+	}
+}
+
+func gnp(n int, p float64, src rand.Source) *simple.UndirectedGraph {
+	g := simple.NewUndirectedGraph()
+	err := gen.Gnp(g, n, p, src)
+	if err != nil {
+		panic(fmt.Sprintf("gnp: bad test: %v", err))
+	}
+	return g
+}
+
+var nodeFilterIteratorTests = []struct {
+	src, filter graph.Nodes
+	root        int64
+	len         int
+}{
+	{src: iterator.NewOrderedNodes([]graph.Node{simple.Node(0)}), filter: graph.Empty, root: 0, len: 0},
+	{src: iterator.NewOrderedNodes([]graph.Node{simple.Node(0), simple.Node(1)}), filter: graph.Empty, root: 0, len: 1},
+	{src: iterator.NewOrderedNodes([]graph.Node{simple.Node(0), simple.Node(1), simple.Node(2)}), filter: iterator.NewOrderedNodes([]graph.Node{simple.Node(1)}), root: 0, len: 1},
+}
+
+func TestNodeFilterIterator(t *testing.T) {
+	for _, test := range nodeFilterIteratorTests {
+		it := graph.NewNodeFilterIterator(test.src, test.filter, test.root)
+		for i := 0; i < 2; i++ {
+			n := it.Len()
+			if n != test.len {
+				t.Errorf("unexpected length of iterator construction/reset: got:%d want:%d", n, test.len)
+			}
+			for it.Next() {
+				n--
+			}
+			if n != 0 {
+				t.Errorf("unexpected remaining nodes after iterator completion: got:%d want:0", n)
+			}
+			it.Reset()
+		}
+	}
+}