feat: add Waxman graph generation support with parameter validation

Author: elecbug

v2/graph/standard/common.go

@@ -21,6 +21,7 @@ const (
 	WattsStrogatz   GraphType = "watts_strogatz"
 	RandomGeometric GraphType = "random_geometric"
 	RandomRegular   GraphType = "random_regular"
+	Waxman          GraphType = "waxman"
 	None            GraphType = "none"
 )
 
@@ -136,6 +137,20 @@ func StandardGraph(seed int, directed bool, weightFunc WeightedFunc, config Grap
 			return nil, fmt.Errorf("invalid parameter 'k' for Random Regular graph")
 		}
 		return RandomRegularGraph(seed, directed, weightFunc, n, k)
+	case Waxman:
+		n, ok := config.Params["n"].(int)
+		if !ok {
+			return nil, fmt.Errorf("invalid parameter 'n' for Waxman graph")
+		}
+		alpha, ok := config.Params["alpha"].(float64)
+		if !ok {
+			return nil, fmt.Errorf("invalid parameter 'alpha' for Waxman graph")
+		}
+		beta, ok := config.Params["beta"].(float64)
+		if !ok {
+			return nil, fmt.Errorf("invalid parameter 'beta' for Waxman graph")
+		}
+		return WaxmanGraph(seed, directed, weightFunc, n, alpha, beta)
 	case None:
 		return graph.New(directed, true), nil
 	default:

v2/graph/standard/waxman.go

@@ -0,0 +1,116 @@
+package standard
+
+import (
+	"fmt"
+	"math"
+
+	"github.com/elecbug/netkit/v2/graph"
+)
+
+type waxmanPoint struct {
+	x float64
+	y float64
+}
+
+func waxmanDistance(a, b waxmanPoint) float64 {
+	dx := a.x - b.x
+	dy := a.y - b.y
+	return math.Sqrt(dx*dx + dy*dy)
+}
+
+// WaxmanGraph generates a Waxman random graph.
+// Nodes are placed uniformly at random in a 2D unit square.
+// For each node pair (u, v), an edge is added with probability:
+//
+//	P(u, v) = alpha * exp(-dist(u, v) / (beta * L))
+//
+// L is the maximum Euclidean distance among all node pairs.
+// alpha controls edge density.
+// beta controls locality sensitivity.
+func WaxmanGraph(seed int, directed bool, weightFunc WeightedFunc, n int, alpha, beta float64) (*graph.Graph, error) {
+	if n < 0 {
+		return nil, fmt.Errorf("invalid number of nodes: n must be non-negative")
+	}
+	if alpha <= 0 || alpha > 1 {
+		return nil, fmt.Errorf("invalid alpha: alpha must be in (0, 1]")
+	}
+	if beta <= 0 || beta > 1 {
+		return nil, fmt.Errorf("invalid beta: beta must be in (0, 1]")
+	}
+
+	r := generateRand(seed)
+	g := graph.New(directed, weightFunc != nil)
+
+	if weightFunc == nil {
+		weightFunc = func(from, to *graph.Node) *graph.Weight {
+			return nil
+		}
+	}
+
+	points := make([]waxmanPoint, n)
+
+	// --- 1. Generate Nodes and Positions ---
+	for i := 0; i < n; i++ {
+		id := graph.NodeID(fmt.Sprintf("%d", i))
+
+		if err := g.AddNode(id); err != nil {
+			return nil, fmt.Errorf("failed to add node: %w", err)
+		}
+
+		points[i] = waxmanPoint{
+			x: r.Float64(),
+			y: r.Float64(),
+		}
+	}
+
+	if n <= 1 {
+		return g, nil
+	}
+
+	// --- 2. Compute L: maximum pairwise distance ---
+	L := 0.0
+
+	for i := 0; i < n; i++ {
+		for j := i + 1; j < n; j++ {
+			d := waxmanDistance(points[i], points[j])
+			if d > L {
+				L = d
+			}
+		}
+	}
+
+	if L == 0 {
+		return g, nil
+	}
+
+	// --- 3. Generate Edges ---
+	for i := 0; i < n; i++ {
+		for j := i + 1; j < n; j++ {
+			d := waxmanDistance(points[i], points[j])
+			p := alpha * math.Exp(-d/(beta*L))
+
+			if r.Float64() >= p {
+				continue
+			}
+
+			from := graph.NodeID(fmt.Sprintf("%d", i))
+			to := graph.NodeID(fmt.Sprintf("%d", j))
+
+			fromNode, err := g.Node(from)
+			if err != nil {
+				return nil, fmt.Errorf("failed to get node: %w", err)
+			}
+
+			toNode, err := g.Node(to)
+			if err != nil {
+				return nil, fmt.Errorf("failed to get node: %w", err)
+			}
+
+			if err := g.AddEdge(from, to, weightFunc(fromNode, toNode)); err != nil {
+				return nil, fmt.Errorf("failed to add edge: %w", err)
+			}
+		}
+	}
+
+	return g, nil
+}