Viterbi.java

package edu.cmu.minorthird.classify.sequential;

import java.util.ArrayList;



// The Viterbi algorithm: find the most probable state path producing
// the observed outputs x

public class Viterbi extends HMMAlgo {
  double[][] v;         // the matrix used to find the decoding
                        // v[i][k] = v_k(i) = 
                        // log(max(P(pi in state k has sym i | path pi)))
  Traceback2[][] B;     // the traceback matrix
  Traceback2 B0;        // the start of the traceback 

  public Viterbi(HMM hmm, String[] x) {
    super(hmm, x);
    final int L = x.length;
    v = new double[L+1][hmm.nstate];
    B = new Traceback2[L+1][hmm.nstate];
    v[0][0] = 0;                // = log(1)
    for (int k=1; k<hmm.nstate; k++)
      v[0][k] = Double.NEGATIVE_INFINITY; // = log(0)
    for (int i=1; i<=L; i++)
      v[i][0] = Double.NEGATIVE_INFINITY; // = log(0)
    for (int i=1; i<=L; i++)
      for (int ell=0; ell<hmm.nstate; ell++) {
        int kmax = 0;
        double maxprod = v[i-1][kmax] + hmm.loga[kmax][ell];
        for (int k=1; k<hmm.nstate; k++) {
          double prod = v[i-1][k] + hmm.loga[k][ell];
          if (prod > maxprod) {
            kmax = k;
            maxprod = prod;
          }
        }
//             System.out.println("x[i-1] is "+x[i-1]);
//             System.out.println(" and Integer.parseInt(x[i-1]) is "+Integer.parseInt(x[i-1]));

        v[i][ell] = hmm.loge[ell][Integer.parseInt(x[i-1])] + maxprod;
        B[i][ell] = new Traceback2(i-1, kmax);
      }
    int kmax = 0;
    double max = v[L][kmax];
    for (int k=1; k<hmm.nstate; k++) {
      if (v[L][k] > max) {
        kmax = k;
        max = v[L][k];
      }
    }
    B0 = new Traceback2(L, kmax);
  }

  public String[] getPath() {
		ArrayList<StringBuffer> p = new ArrayList<StringBuffer>(); 
		
    Traceback2 tb = B0;
    int i = tb.i, j = tb.j;
    int idx = 0;
    while ((tb = B[tb.i][tb.j]) != null) {
	    StringBuffer tt = new StringBuffer();
	    tt.append(hmm.state[j]);
			p.add( tt.reverse() );
			idx ++;
      i = tb.i; j = tb.j;
    }        
    String[] y = new String[p.size()];
    for ( i=0;i< p.size(); i++){
//    	System.out.println("i is "+i+ " and p.size() is "+p.size()+" and p.get is "+p.get(i));
//     y[i] = ""+p.get(i);
     y[i] = p.get(i).toString();
     System.out.println("y["+i+"] is now " + y[i]);

    }
    
    return y;
  }

    /*public void print(Output out) {
    for (int j=0; j<hmm.nstate; j++) {
      for (int i=0; i<v.length; i++)
        out.print(HMM.fmtlog(v[i][j]));
      out.println();
    }
    }*/
}