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/
dense_undirected_matrix.go
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/
dense_undirected_matrix.go
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// Copyright ©2014 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 concrete
import (
"github.com/gonum/graph"
"github.com/gonum/matrix/mat64"
)
// UndirectedDenseGraph represents a graph such that all IDs are in a contiguous
// block from 0 to n-1.
type UndirectedDenseGraph struct {
absent float64
mat *mat64.SymDense
}
// NewUndirectedDenseGraph creates an undirected dense graph with n nodes.
// If passable is true all pairs of nodes will be connected by an edge
// with unit cost, otherwise every node will start unconnected with
// the cost specified by absent.
func NewUndirectedDenseGraph(n int, passable bool, absent float64) *UndirectedDenseGraph {
mat := make([]float64, n*n)
v := 1.
if !passable {
v = absent
}
for i := range mat {
mat[i] = v
}
return &UndirectedDenseGraph{mat: mat64.NewSymDense(n, mat), absent: absent}
}
func (g *UndirectedDenseGraph) Has(n graph.Node) bool {
id := n.ID()
r := g.mat.Symmetric()
return 0 <= id && id < r
}
func (g *UndirectedDenseGraph) Nodes() []graph.Node {
r := g.mat.Symmetric()
nodes := make([]graph.Node, r)
for i := 0; i < r; i++ {
nodes[i] = Node(i)
}
return nodes
}
func (g *UndirectedDenseGraph) Edges() []graph.Edge {
var edges []graph.Edge
r, _ := g.mat.Dims()
for i := 0; i < r; i++ {
for j := i + 1; j < r; j++ {
if !isSame(g.mat.At(i, j), g.absent) {
edges = append(edges, Edge{Node(i), Node(j)})
}
}
}
return edges
}
func (g *UndirectedDenseGraph) Degree(n graph.Node) int {
id := n.ID()
var deg int
r := g.mat.Symmetric()
for i := 0; i < r; i++ {
if i == id {
continue
}
if !isSame(g.mat.At(id, i), g.absent) {
deg++
}
}
return deg
}
func (g *UndirectedDenseGraph) From(n graph.Node) []graph.Node {
var neighbors []graph.Node
id := n.ID()
r := g.mat.Symmetric()
for i := 0; i < r; i++ {
if i == id {
continue
}
if !isSame(g.mat.At(id, i), g.absent) {
neighbors = append(neighbors, Node(i))
}
}
return neighbors
}
func (g *UndirectedDenseGraph) HasEdge(u, v graph.Node) bool {
uid := u.ID()
vid := v.ID()
return uid != vid && !isSame(g.mat.At(uid, vid), g.absent)
}
func (g *UndirectedDenseGraph) Edge(u, v graph.Node) graph.Edge {
return g.EdgeBetween(u, v)
}
func (g *UndirectedDenseGraph) EdgeBetween(u, v graph.Node) graph.Edge {
if g.HasEdge(u, v) {
return Edge{u, v}
}
return nil
}
func (g *UndirectedDenseGraph) Weight(e graph.Edge) float64 {
return g.mat.At(e.From().ID(), e.To().ID())
}
func (g *UndirectedDenseGraph) SetEdgeWeight(e graph.Edge, weight float64) {
fid := e.From().ID()
tid := e.To().ID()
if fid == tid {
panic("concrete: set edge cost of illegal edge")
}
g.mat.SetSym(fid, tid, weight)
}
func (g *UndirectedDenseGraph) RemoveEdge(e graph.Edge) {
g.mat.SetSym(e.From().ID(), e.To().ID(), g.absent)
}
func (g *UndirectedDenseGraph) Matrix() mat64.Matrix {
// Prevent alteration of dimensions of the returned matrix.
m := *g.mat
return &m
}