implement checking if graph is an absorbing markov chain

cmd/internal/markov/absorbing.go

@@ -0,0 +1,107 @@
+/*
+Copyright © 2025 filifa
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+package markov
+
+import (
+	"errors"
+	"math"
+	"strconv"
+
+	"gonum.org/v1/gonum/graph"
+	"gonum.org/v1/gonum/graph/encoding"
+	"gonum.org/v1/gonum/graph/simple"
+)
+
+type AbsorbingMarkovChain struct {
+	*simple.WeightedDirectedGraph
+}
+
+func NewAbsorbingMarkovChain() *AbsorbingMarkovChain {
+	return &AbsorbingMarkovChain{WeightedDirectedGraph: simple.NewWeightedDirectedGraph(math.NaN(), math.NaN())}
+}
+
+func (g *AbsorbingMarkovChain) IsValid() bool {
+	for nodes := g.Nodes(); nodes.Next(); {
+		u := nodes.Node().(*node)
+
+		if g.From(u.ID()).Len() == 0 {
+			continue
+		}
+
+		if g.outWeightSum(u) != 1 {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (g *AbsorbingMarkovChain) outWeightSum(u *node) float64 {
+	sum := 0.0
+	for nodes := g.From(u.ID()); nodes.Next(); {
+		v := nodes.Node()
+		e := g.WeightedEdge(u.ID(), v.ID())
+		if e != nil {
+			sum += e.(*weightedEdge).W
+		}
+	}
+
+	return sum
+}
+
+func (g *AbsorbingMarkovChain) NewEdge(from, to graph.Node) graph.Edge {
+	e := g.WeightedDirectedGraph.NewWeightedEdge(from, to, math.NaN()).(simple.WeightedEdge)
+	return &weightedEdge{WeightedEdge: e}
+}
+
+func (g *AbsorbingMarkovChain) NewNode() graph.Node {
+	return &node{Node: g.WeightedDirectedGraph.NewNode()}
+}
+
+func (g *AbsorbingMarkovChain) SetEdge(e graph.Edge) {
+	g.WeightedDirectedGraph.SetWeightedEdge(e.(*weightedEdge))
+}
+
+type weightedEdge struct {
+	simple.WeightedEdge
+}
+
+func (e *weightedEdge) SetAttribute(attr encoding.Attribute) error {
+	var err error
+
+	switch attr.Key {
+	case "weight":
+		e.W, err = strconv.ParseFloat(attr.Value, 64)
+	default:
+		err = errors.New("unknown key" + attr.Key)
+	}
+
+	return err
+}
+
+type node struct {
+	graph.Node
+	dotID string
+}
+
+func (n *node) SetDOTID(id string) {
+	n.dotID = id
+}
+
+func (n *node) DOTID() string {
+	return n.dotID
+}

cmd/root.go

@@ -19,10 +19,13 @@ package cmd
 import (
 	"os"
 
+	"scm.dairydemon.net/filifa/dptdist/cmd/internal/markov"
+
 	"github.com/spf13/cobra"
+	"gonum.org/v1/gonum/graph/encoding/dot"
 )
 
-
+var file string
 
 // rootCmd represents the base command when called without any subcommands
 var rootCmd = &cobra.Command{
@@ -36,7 +39,24 @@ This application is a tool to generate the needed files
 to quickly create a Cobra application.`,
 	// Uncomment the following line if your bare application
 	// has an action associated with it:
-	// Run: func(cmd *cobra.Command, args []string) { },
+	Run: parse,
+}
+
+func parse(cmd *cobra.Command, args []string) {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		panic(err)
+	}
+
+	graph := markov.NewAbsorbingMarkovChain()
+	err = dot.Unmarshal(data, graph)
+	if err != nil {
+		panic(err)
+	}
+
+	if !graph.IsValid() {
+		panic("not an absorbing Markov chain!")
+	}
 }
 
 // Execute adds all child commands to the root command and sets flags appropriately.
@@ -58,6 +78,7 @@ func init() {
 	// Cobra also supports local flags, which will only run
 	// when this action is called directly.
 	rootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+
+	rootCmd.Flags().StringVarP(&file, "file", "f", "", "dot file with absorbing Markov chain")
+	rootCmd.MarkFlagRequired("file")
 }
-
-