Introduction to Lattice
Arcs in a Lattice are of type LatticeArc, whose weight is of type LatticeWeight.
A LatticeWeight has two parts:
value1: It contains the graph cost
value2: It contains the acoustic cost
The following code demonstrates how to create and visualize a lattice.
1#!/usr/bin/env python3
2
3import graphviz
4
5import kaldifst
6
7fst = kaldifst.Lattice()
8s0 = fst.add_state()
9s1 = fst.add_state()
10s2 = fst.add_state()
11s3 = fst.add_state()
12
13fst.start = s0
14fst.add_arc(
15 state=s0,
16 arc=kaldifst.LatticeArc(
17 ilabel=1,
18 olabel=2,
19 weight=kaldifst.LatticeWeight(graph_cost=0.1, acoustic_cost=0.2),
20 nextstate=s1,
21 ),
22)
23
24fst.add_arc(
25 state=s0,
26 arc=kaldifst.LatticeArc(
27 ilabel=3,
28 olabel=4,
29 weight=kaldifst.LatticeWeight(graph_cost=0.3, acoustic_cost=0.4),
30 nextstate=s2,
31 ),
32)
33
34fst.add_arc(
35 state=s1,
36 arc=kaldifst.LatticeArc(
37 ilabel=5,
38 olabel=6,
39 weight=kaldifst.LatticeWeight(graph_cost=0.5, acoustic_cost=0.6),
40 nextstate=s3,
41 ),
42)
43
44fst.add_arc(
45 state=s2,
46 arc=kaldifst.LatticeArc(
47 ilabel=6,
48 olabel=8,
49 weight=kaldifst.LatticeWeight(graph_cost=0.7, acoustic_cost=0.8),
50 nextstate=s3,
51 ),
52)
53
54fst.set_final(state=s3, weight=kaldifst.LatticeWeight.one)
55
56print(fst)
57# The above statement gives the following output
58"""
590 1 1 2 0.1,0.2
600 2 3 4 0.3,0.4
611 3 5 6 0.5,0.6
622 3 6 8 0.7,0.8
633
64"""
65
66# Now we can draw it
67fst_dot = kaldifst.draw(fst, acceptor=False, portrait=True)
68print(fst_dot)
69# You can use
70# https://dreampuf.github.io/GraphvizOnline
71# to visualize it and share the link to others
72
73# Alternatively, you can use graphviz to visualize it
74source = graphviz.Source(fst_dot)
75source.render(outfile="lattice.svg")
Fig. 9 lattice.svg generated from the above code.
1:2/0.1,0.2 means:
The input label is 1
The output label is 2
The graph cost is 0.1
The acoustic cost is 0.2