There are two top-level scripts in this directory which demonstrate
  end-to-end (specifically single-stage flat-start) LF-MMI (i.e. chain)
  training. "run_end2end_phone.sh" is basically like "../run.sh"
  except it does not train any GMM or SGMM models and after doing data/dict
  preparation and feature extraction goes straight to flat-start chain training.
  It uses a phoneme-based lexicon just like "../run.sh" does.
  "run_end2end_char.sh" is exactly like "run_end2end_phone.sh" excpet it
  uses a trivial grapheme-based (i.e. character-based) lexicon.
  For details please see the comments at top of local/chain/e2e/run_flatstart_*.sh
  and also src/chain/chain-generic-numerator.h.