/**
* /// Determinizes an fst. The result will be an equivalent fst that has the
* /// property that no state has two transitions with the same input label. For
* /// this algorithm, epsilon transitions are treated as regular symbols.
* ///
* /// @param fst the fst to determinize
* /// @return the determinized fst
*/
public static Fst Get(Fst fst)
{
if (fst.Semiring == null)
{
// semiring not provided
return(null);
}
// initialize the queue and new fst
Semiring semiring = fst.Semiring;
Fst res = new Fst(semiring);
res.Isyms = fst.Isyms;
res.Osyms = fst.Osyms;
// stores the queue (item in index 0 is next)
Queue <List <Pair <State, float> > > queue = new Queue <List <Pair <State, float> > >();
Dictionary <String, State> stateMapper = new Dictionary <String, State>();
State s = new State(semiring.Zero);
string stateString = "(" + fst.Start + "," + semiring.One + ")";
queue.Enqueue(new List <Pair <State, float> >());
queue.Peek().Add(new Pair <State, float>(fst.Start, semiring.One));
res.AddState(s);
stateMapper.Add(stateString, s);
res.SetStart(s);
while (queue.Count != 0)
{
List <Pair <State, float> > p = queue.Dequeue();
State pnew = GetStateLabel(p, stateMapper);
//queueRemoveAt(0);
List <int> labels = GetUniqueLabels(fst, p);
foreach (int label in labels)
{
float wnew = semiring.Zero;
// calc w'
foreach (Pair <State, float> ps in p)
{
State old = ps.GetLeft();
float u = ps.GetRight();
int numArcs = old.GetNumArcs();
for (int j = 0; j < numArcs; j++)
{
Arc arc = old.GetArc(j);
if (label == arc.Ilabel)
{
wnew = semiring.Plus(wnew,
semiring.Times(u, arc.Weight));
}
}
}
// calc new states
// keep residual weights to variable forQueue
List <Pair <State, float> > forQueue = new List <Pair <State, float> >();
foreach (Pair <State, float> ps in p)
{
State old = ps.GetLeft();
float u = ps.GetRight();
float wnewRevert = semiring.Divide(semiring.One, wnew);
int numArcs = old.GetNumArcs();
for (int j = 0; j < numArcs; j++)
{
Arc arc = old.GetArc(j);
if (label == arc.Ilabel)
{
State oldstate = arc.NextState;
Pair <State, float> pair = GetPair(forQueue,
oldstate, semiring.Zero);
pair.SetRight(semiring.Plus(
pair.GetRight(),
semiring.Times(wnewRevert,
semiring.Times(u, arc.Weight))));
}
}
}
// build new state's id and new elements for queue
string qnewid = "";
foreach (Pair <State, float> ps in forQueue)
{
State old = ps.GetLeft();
float unew = ps.GetRight();
if (!qnewid.Equals(""))
{
qnewid = qnewid + ",";
}
qnewid = qnewid + "(" + old + "," + unew + ")";
}
if (stateMapper.Get(qnewid) == null)
{
State qnew = new State(semiring.Zero);
res.AddState(qnew);
stateMapper.Add(qnewid, qnew);
// update new state's weight
float fw = qnew.FinalWeight;
foreach (Pair <State, float> ps in forQueue)
{
fw = semiring.Plus(fw, semiring.Times(ps.GetLeft().FinalWeight, ps.GetRight()));
}
qnew.FinalWeight = fw;
queue.Enqueue(forQueue);
}
pnew.AddArc(new Arc(label, label, wnew, stateMapper[qnewid]));
}
}
return(res);
}
