维特比算法

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

 

namespace Viterbi

{

    class Program

    {

        //Weather states

        static String HEALTHY = "Healthy";

        static String FEVER = "Fever";

        //Dependable actions (observations)

        static String DIZZY = "dizzy";

        static String COLD = "cold";

        static String NORMAL = "normal";

 

        static void Main(string[] args)

        {

            //initialize our arrays of states and observations

            String[] states = { HEALTHY, FEVER };

            String[] observations = { DIZZY, COLD, NORMAL };

 

            var start_probability = new Dictionary<String, float>();

            start_probability.Add(HEALTHY, 0.6f);

            start_probability.Add(FEVER, 0.4f);

            //Transition probability

            var transition_probability = new Dictionary<String, Dictionary<String, float>>();

            var t1 = new Dictionary<String, float>();

            t1.Add(HEALTHY, 0.7f);

            t1.Add(FEVER, 0.3f);

            Dictionary<String, float> t2 = new Dictionary<String, float>();

            t2.Add(HEALTHY, 0.4f);

            t2.Add(FEVER, 0.6f);

            transition_probability.Add(HEALTHY, t1);

            transition_probability.Add(FEVER, t2);

 

            //emission_probability

            var emission_probability = new Dictionary<String, Dictionary<String, float>>();

            var e1 = new Dictionary<String, float>();

            e1.Add(DIZZY, 0.1f);

            e1.Add(COLD, 0.4f);

            e1.Add(NORMAL, 0.5f);

 

            Dictionary<String, float> e2 = new Dictionary<String, float>();

            e2.Add(DIZZY, 0.6f);

            e2.Add(COLD, 0.3f);

            e2.Add(NORMAL, 0.1f);

 

            emission_probability.Add(HEALTHY, e1);

            emission_probability.Add(FEVER, e2);

 

            Object[] ret = forward_viterbi(observations, states, start_probability, transition_probability, emission_probability);

            Console.WriteLine((float)ret[0]);

            Console.WriteLine((String)ret[1]);

            Console.WriteLine((float)ret[2]);

            Console.ReadLine();

 

        }

 

        public static Object[] forward_viterbi(String[] obs, String[] states, Dictionary<String, float> start_p, Dictionary<String, Dictionary<String, float>> trans_p, Dictionary<String, Dictionary<String, float>> emit_p)

        {

 

            var T = new Dictionary<String, Object[]>();

            foreach (String state in states)

            {

                T.Add(state, new Object[] { start_p[state], state, start_p[state] });

            }

 

 

            foreach (String output in obs)

            {

                var U = new Dictionary<String, Object[]>();

 

                foreach (String next_state in states)

                {

                    float total = 0;

                    String argmax = "";

                    float valmax = 0;

 

                    float prob = 1;

                    String v_path = "";

                    float v_prob = 1;

 

                    foreach (String source_state in states)

                    {

 

                        Object[] objs = T[source_state];

                        prob = ((float)objs[0]);

                        v_path = (String)objs[1];

                        v_prob = ((float)objs[2]);

 

                        float p = emit_p[source_state][output] * trans_p[source_state][next_state];

                        prob *= p;

                        v_prob *= p;

                        total += prob;

 

                        if (v_prob > valmax)

                        {

                            argmax = v_path + "," + next_state;

                            valmax = v_prob;

                        }

                    }

                    U.Add(next_state, new Object[] { total, argmax, valmax });

                }

                T = U;

            }

 

 

 

 

 

 

            float xtotal = 0;

            String xargmax = "";

            float xvalmax = 0;

 

            float xprob;

            String xv_path;

            float xv_prob;

 

            foreach (String state in states)

            {

                Object[] objs = T[state];

                xprob = ((float)objs[0]);

                xv_path = ((String)objs[1]);

                xv_prob = ((float)objs[2]);

 

                xtotal += xprob;

                if (xv_prob > xvalmax)

                {

                    xargmax = xv_path;

                    xvalmax = xv_prob;

                }

            }

            return new Object[] { xtotal, xargmax, xvalmax };

 

 

        }

    }

}