visualize FSA via GraphViz.

[csukuangfj]

I know it's difficult, if not impossible, to visualize an FSA with lots of states and transitions.

Visualization can be helpful to debug later algorithms, such as epsilon removal, trim, determinization ... ...

---

Visualization of the following fsa is given below.

  std::vector<Arc> arcs = {
      {0, 1, 2}, {0, 2, 1}, {1, 2, 0}, {1, 3, 5}, {2, 3, 6},
  };
  std::vector<Range> leaving_arcs = {
      {0, 2}, {2, 4}, {4, 5}, {0, 0},  // the last state has no leaving arcs
  };

It is obtained by

./k2/csrc/fsa_renderer_test 2>&1 >/dev/null | dot -Tpng > abc.png

[danpovey]

Great! Merging.