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graph/path: indicate negative cycle weights with -Inf instead of NaN

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The paths are undefined, but the limit of the path weight is -Inf.
This commit is contained in:
Dan Kortschak
2019-02-07 20:57:33 +10:30
parent 936e3fec9e
commit ee7dd3742a
3 changed files with 14 additions and 14 deletions
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12
graph/path/shortest.go
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@@ -119,7 +119,7 @@ func (p Shortest) WeightTo(vid int64) float64 {
// To returns a shortest path to v and the weight of the path. If the path
// to v includes a negative cycle, one pass through the cycle will be included
// in path and weight will be returned as NaN.
// in path and weight will be returned as -Inf.
func (p Shortest) To(vid int64) (path []graph.Node, weight float64) {
to, toOK := p.indexOf[vid]
if !toOK || math.IsInf(p.dist[to], 1) {
@@ -133,7 +133,7 @@ func (p Shortest) To(vid int64) (path []graph.Node, weight float64) {
seen.Add(from)
for to != from {
if seen.Has(to) {
weight = math.NaN()
weight = math.Inf(-1)
break
}
seen.Add(to)
@@ -253,7 +253,7 @@ func (p AllShortest) Weight(uid, vid int64) float64 {
// one shortest path exists between u and v, a randomly chosen path will be returned and
// unique is returned false. If a cycle with zero weight exists in the path, it will not
// be included, but unique will be returned false. If a negative cycle exists on the path
// from u to v, path will be returned nil, weight will be NaN and unique will be false.
// from u to v, path will be returned nil, weight will be -Inf and unique will be false.
func (p AllShortest) Between(uid, vid int64) (path []graph.Node, weight float64, unique bool) {
from, fromOK := p.indexOf[uid]
to, toOK := p.indexOf[vid]
@@ -265,7 +265,7 @@ func (p AllShortest) Between(uid, vid int64) (path []graph.Node, weight float64,
}
weight = p.dist.At(from, to)
if math.IsNaN(weight) {
if math.IsInf(weight, -1) {
return nil, weight, false
}
@@ -314,7 +314,7 @@ func (p AllShortest) Between(uid, vid int64) (path []graph.Node, weight float64,
// AllBetween returns all shortest paths from u to v and the weight of the paths. Paths
// containing zero-weight cycles are not returned. If a negative cycle exists between
// u and v, paths is returned nil and weight is returned as NaN.
// u and v, paths is returned nil and weight is returned as -Inf.
func (p AllShortest) AllBetween(uid, vid int64) (paths [][]graph.Node, weight float64) {
from, fromOK := p.indexOf[uid]
to, toOK := p.indexOf[vid]
@@ -326,7 +326,7 @@ func (p AllShortest) AllBetween(uid, vid int64) (paths [][]graph.Node, weight fl
}
weight = p.dist.At(from, to)
if math.IsNaN(weight) {
if math.IsInf(weight, -1) {
return nil, weight
}