def beam_search(decoder: nn.Module,
enc_out: th.Tensor,
lm: Optional[LmType] = None,
ctc_prob: Optional[th.Tensor] = None,
lm_weight: float = 0,
beam_size: int = 8,
nbest: int = 1,
max_len: int = -1,
max_len_ratio: float = 1,
min_len: int = 0,
min_len_ratio: float = 0,
sos: int = -1,
eos: int = -1,
unk: int = -1,
len_norm: bool = True,
ctc_weight: float = 0,
end_detect: bool = False,
len_penalty: float = 0,
cov_penalty: float = 0,
temperature: float = 1,
allow_partial: bool = False,
cov_threshold: float = 0.5,
eos_threshold: float = 0) -> List[Dict]:
"""
Vectorized beam search algothrim for transformer decoder
Args
enc_out (Tensor): T x 1 x F, encoder output
"""
if sos < 0 or eos < 0:
raise RuntimeError(f"Invalid SOS/EOS ID: {sos:d}/{eos:d}")
T, N, D_enc = enc_out.shape
if N != 1:
raise RuntimeError(
f"Got batch size {N:d}, now only support one utterance")
if not hasattr(decoder, "step"):
raise RuntimeError("Function step should defined in decoder network")
if beam_size > decoder.vocab_size:
raise RuntimeError(f"Beam size({beam_size}) > vocabulary size")
min_len = max(min_len, int(min_len_ratio * T))
max_len = min(max_len, int(max_len_ratio * T)) if max_len_ratio > 0 else T
logger.info(f"--- shape of the encoder output: {T} x {D_enc}")
logger.info("--- length constraint of the decoding " +
f"sequence: ({min_len}, {max_len})")
nbest = min(beam_size, nbest)
device = enc_out.device
# cov_* are diabled
beam_param = BeamSearchParam(beam_size=beam_size,
sos=sos,
eos=eos,
unk=unk,
device=device,
min_len=min_len,
max_len=max_len,
len_norm=len_norm,
lm_weight=lm_weight,
ctc_weight=ctc_weight,
end_detect=end_detect,
len_penalty=len_penalty,
allow_partial=allow_partial,
eos_threshold=eos_threshold,
ctc_beam_size=int(beam_size * 1.5))
beam_tracker = BeamTracker(beam_param, ctc_prob=ctc_prob)
pre_emb = None
lm_state = None
# T x 1 x D => T x beam x D
enc_out = th.repeat_interleave(enc_out, beam_size, 1)
# step by step
stop = False
while not stop:
# beam
pre_tok, point = beam_tracker[-1]
# beam x V
dec_out, pre_emb = decoder.step(
enc_out,
pre_tok[:, None],
out_idx=-1,
pre_emb=None if pre_emb is None else pre_emb[:, point])
# compute prob: beam x V, nagetive
am_prob = tf.log_softmax(dec_out / temperature, dim=-1)
if lm and beam_param.lm_weight > 0:
# beam x V
lm_prob, lm_state = lm_score_impl(lm, point, pre_tok, lm_state)
else:
lm_prob = 0
# one beam search step
stop = beam_tracker.step(am_prob, lm_prob)
# return nbest
return beam_tracker.nbest_hypos(nbest)
def beam_search(decoder: nn.Module,
att_net: nn.Module,
enc_out: th.Tensor,
lm: Optional[LmType] = None,
lm_weight: float = 0,
beam_size: int = 8,
nbest: int = 1,
max_len: int = -1,
max_len_ratio: float = 1,
min_len: int = 0,
min_len_ratio: float = 0,
sos: int = -1,
eos: int = -1,
len_norm: bool = True,
len_penalty: float = 0,
cov_penalty: float = 0,
temperature: float = 1,
cov_threshold: float = 0.5,
eos_threshold: float = 1) -> List[Dict]:
"""
Vectorized beam search algothrim (see batch version beam_search_batch)
Args
att_net (nn.Module): attention network
enc_out (Tensor): 1 x T x F, encoder output
"""
if sos < 0 or eos < 0:
raise RuntimeError(f"Invalid SOS/EOS ID: {sos:d}/{eos:d}")
N, T, D_enc = enc_out.shape
if N != 1:
raise RuntimeError(
f"Got batch size {N:d}, now only support one utterance")
if not hasattr(decoder, "step"):
raise RuntimeError("Function step should defined in decoder network")
if beam_size > decoder.vocab_size:
raise RuntimeError(f"Beam size({beam_size}) > vocabulary size")
min_len = max(min_len, int(min_len_ratio * T))
max_len = min(max_len, int(max_len_ratio * T))
logger.info(f"--- shape of the encoder output: {T} x {D_enc}")
logger.info("--- length constraint of the decoding " +
f"sequence: ({min_len}, {max_len})")
nbest = min(beam_size, nbest)
device = enc_out.device
att_ali = None
dec_hid = None
# N x T x F => N*beam x T x F
enc_out = th.repeat_interleave(enc_out, beam_size, 0)
att_ctx = th.zeros([N * beam_size, D_enc], device=device)
proj = th.zeros([N * beam_size, D_enc], device=device)
beam_param = BeamSearchParam(beam_size=beam_size,
sos=sos,
eos=eos,
device=device,
min_len=min_len,
max_len=max_len,
len_norm=len_norm,
lm_weight=lm_weight,
len_penalty=len_penalty,
cov_penalty=cov_penalty,
cov_threshold=cov_threshold,
eos_threshold=eos_threshold)
beam_tracker = BeamTracker(beam_param)
lm_state = None
# clear states
att_net.clear()
# step by step
stop = False
while not stop:
# beam
pre_tok, point = beam_tracker[-1]
# step forward
dec_hid = adjust_hidden(point, dec_hid)
att_ali = None if att_ali is None else att_ali[point]
dec_out, att_ctx, dec_hid, att_ali, proj = decoder.step(
att_net,
pre_tok,
enc_out,
att_ctx[point],
dec_hid=dec_hid,
att_ali=att_ali,
proj=proj[point])
# compute prob: beam x V, nagetive
am_prob = tf.log_softmax(dec_out / temperature, dim=-1)
if lm and beam_param.lm_weight > 0:
# beam x V
lm_prob, lm_state = lm_score_impl(lm, point, pre_tok, lm_state)
else:
lm_prob = 0
# one beam search step
stop = beam_tracker.step(am_prob, lm_prob, att_ali=att_ali)
# return nbest
return beam_tracker.nbest_hypos(nbest)