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 };
 
 
        }
    }
}