add tests for if graph is absorbing markov chain

cmd/internal/markov/absorbing.go

@@ -25,6 +25,7 @@ import (
 	"gonum.org/v1/gonum/graph/encoding"
 	"gonum.org/v1/gonum/graph/multi"
 	"gonum.org/v1/gonum/graph/simple"
+	"gonum.org/v1/gonum/graph/topo"
 	"gonum.org/v1/gonum/mat"
 )
 
@@ -79,6 +80,32 @@ func (g *AbsorbingMarkovChain) AbsorbingNodes() []graph.Node {
 	return absorbingNodes
 }
 
+func (g *AbsorbingMarkovChain) IsAbsorbing() bool {
+	absorbingNodes := g.AbsorbingNodes()
+	if len(absorbingNodes) == 0 {
+		return false
+	}
+
+	for nodes := g.Nodes(); nodes.Next(); {
+		u := nodes.Node()
+		if !g.canBeAbsorbed(u, absorbingNodes) {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (g *AbsorbingMarkovChain) canBeAbsorbed(u graph.Node, absorbingNodes []graph.Node) bool {
+	for _, v := range absorbingNodes {
+		if topo.PathExistsIn(g, u, v) {
+			return true
+		}
+	}
+
+	return false
+}
+
 func (g *AbsorbingMarkovChain) AdjacencyMatrix() mat.Matrix {
 	adj := simple.NewDirectedMatrix(g.Nodes().Len(), 0, 0, 0)
 	for edges := g.WeightedEdges(); edges.Next(); {

cmd/root.go

@@ -57,6 +57,10 @@ func parse(cmd *cobra.Command, args []string) {
 	}
 
 	if !graph.IsValid() {
+		panic("not a Markov chain!")
+	}
+
+	if !graph.IsAbsorbing() {
 		panic("not an absorbing Markov chain!")
 	}