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sample.py
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Fri, May 3, 07:54

sample.py
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import tensorflow as tf
import model
def top_k_logits(logits, k):
if k == 0:
# no truncation
return logits
def _top_k():
values, _ = tf.nn.top_k(logits, k=k)
min_values = values[:, -1, tf.newaxis]
return tf.where(
logits < min_values,
tf.ones_like(logits, dtype=logits.dtype) * -1e10,
logits,
)
return tf.cond(
tf.equal(k, 0),
lambda: logits,
lambda: _top_k(),
)
def top_p_logits(logits, p):
"""Nucleus sampling"""
batch, _ = logits.shape.as_list()
sorted_logits = tf.sort(logits, direction='DESCENDING', axis=-1)
cumulative_probs = tf.cumsum(tf.nn.softmax(sorted_logits, axis=-1), axis=-1)
indices = tf.stack([
tf.range(0, batch),
# number of indices to include
tf.maximum(tf.reduce_sum(tf.cast(cumulative_probs <= p, tf.int32), axis=-1) - 1, 0),
], axis=-1)
min_values = tf.gather_nd(sorted_logits, indices)
return tf.where(
logits < min_values,
tf.ones_like(logits) * -1e10,
logits,
)
def sample_sequence(*, hparams, length, start_token=None, batch_size=None, context=None, temperature=1, top_k=0, top_p=1):
if start_token is None:
assert context is not None, 'Specify exactly one of start_token and context!'
else:
assert context is None, 'Specify exactly one of start_token and context!'
context = tf.fill([batch_size, 1], start_token)
def step(hparams, tokens, past=None):
lm_output = model.model(hparams=hparams, X=tokens, past=past, reuse=tf.AUTO_REUSE)
logits = lm_output['logits'][:, :, :hparams.n_vocab]
presents = lm_output['present']
presents.set_shape(model.past_shape(hparams=hparams, batch_size=batch_size))
return {
'logits': logits,
'presents': presents,
}
with tf.name_scope('sample_sequence'):
def body(past, prev, output):
next_outputs = step(hparams, prev, past=past)
logits = next_outputs['logits'][:, -1, :] / tf.to_float(temperature)
logits = top_k_logits(logits, k=top_k)
logits = top_p_logits(logits, p=top_p)
samples = tf.multinomial(logits, num_samples=1, output_dtype=tf.int32)
return [
next_outputs['presents'] if past is None else tf.concat([past, next_outputs['presents']], axis=-2),
samples,
tf.concat([output, samples], axis=1)
]
past, prev, output = body(None, context, context)
def cond(*args):
return True
_, _, tokens = tf.while_loop(
cond=cond, body=body,
maximum_iterations=length - 1,
loop_vars=[
past,
prev,
output
],
shape_invariants=[
tf.TensorShape(model.past_shape(hparams=hparams, batch_size=batch_size)),
tf.TensorShape([batch_size, None]),
tf.TensorShape([batch_size, None]),
],
back_prop=False,
)
return tokens

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