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import tensorflow as tf | |
from tensorflow.keras.layers import Dense, Dropout, Embedding, LayerNormalization, Layer, Flatten | |
from tensorflow.keras.models import Model | |
import numpy as np | |
class PositionalEncoder(Layer): | |
def __init__(self, name = "Positional_Encoder"): | |
super(PositionalEncoder, self).__init__(name = name) | |
def get_angles(self, pos, i, d_model): # pos: (seq_length, 1) i: (1, d_model) | |
angles = 1 / np.power(10000., (2*(i//2)) / np.float32(d_model)) | |
return pos * angles # (seq_length, d_model) | |
def call(self, inputs): | |
seq_length = inputs.shape.as_list()[-2] | |
d_model = inputs.shape.as_list()[-1] | |
angles = self.get_angles(np.arange(seq_length)[:, np.newaxis], | |
np.arange(d_model)[np.newaxis, :], | |
d_model) | |
angles[:, 0::2] = np.sin(angles[:, 0::2]) | |
angles[:, 1::2] = np.cos(angles[:, 1::2]) | |
pos_encoding = angles[np.newaxis, ...] | |
return inputs + tf.cast(pos_encoding, tf.float32) | |
class ScaledDotProductAttention(Layer): | |
def __init__(self, name = "Attention"): | |
super(ScaledDotProductAttention, self).__init__(name = name) | |
def call(self, queries, keys, values, mask): | |
product = tf.matmul(queries, keys, transpose_b = True) | |
keys_dim = tf.cast(tf.shape(keys)[-1], dtype = tf.float32) | |
scaled_product = product / tf.math.sqrt(keys_dim) | |
if mask is not None: | |
scaled_product += (mask * -1e9) | |
attention = tf.matmul(tf.nn.softmax(scaled_product, axis = -1), values) | |
return attention | |
class MultiHeadAttention(Layer): | |
def __init__(self, nb_proj, name = "Multi_Head_Attention"): | |
super(MultiHeadAttention, self).__init__(name = name) | |
self.nb_proj = nb_proj | |
def build(self, input_shape): | |
self.d_model = input_shape[-1] | |
assert self.d_model % self.nb_proj == 0 | |
self.d_proj = self.d_model // self.nb_proj | |
self.Query_Dense = Dense(units = self.d_model) | |
self.Key_Dense = Dense(units = self.d_model) | |
self.Value_Dense = Dense(units = self.d_model) | |
self.Final_Dense = Dense(units = self.d_model) | |
self.Attention = ScaledDotProductAttention() | |
def split_proj(self, inputs, batch_size): # inputs: (batch_size, seq_length, d_model) | |
shape = (batch_size, | |
-1, | |
self.nb_proj, | |
self.d_proj) | |
splitted_inputs = tf.reshape(inputs, shape = shape) # (batch_size, seq_length, nb_proj, d_proj) | |
return tf.transpose(splitted_inputs, perm = [0, 2, 1, 3]) # (batch_size, nb_proj, seq_length, d_proj) | |
def call(self, queries, keys, values, mask): | |
batch_size = tf.shape(queries)[0] | |
queries = self.Query_Dense(queries) | |
keys = self.Key_Dense(keys) | |
values = self.Value_Dense(values) | |
queries = self.split_proj(queries, batch_size) | |
keys = self.split_proj(keys, batch_size) | |
values = self.split_proj(values, batch_size) | |
attention = self.Attention(queries, keys, values, mask) | |
attention = tf.transpose(attention, perm = [0, 2, 1, 3]) # (batch_size, seq_length, nb_proj, d_proj) | |
concat_attention = tf.reshape(attention, shape = (batch_size, -1, self.d_model)) | |
outputs = self.Final_Dense(concat_attention) | |
return outputs | |
class EncoderLayer(Layer): | |
def __init__(self, FFN_units, nb_proj, dropout_rate, name = "Encoder_Layer"): | |
super(EncoderLayer, self).__init__(name = name) | |
self.FFN_units = FFN_units | |
self.nb_proj = nb_proj | |
self.dropout_rate = dropout_rate | |
def build(self, input_shape): | |
self.d_model = input_shape[-1] | |
self.multi_head_attention = MultiHeadAttention(self.nb_proj) | |
self.dropout_1 = Dropout(rate = self.dropout_rate) | |
self.norm_1 = LayerNormalization(epsilon = 1e-6) | |
self.Dense_1 = Dense(units = self.FFN_units, activation = "relu") | |
self.Dense_2 = Dense(units = self.d_model) | |
self.dropout_2 = Dropout(rate = self.dropout_rate) | |
self.norm_2 = LayerNormalization(epsilon = 1e-6) | |
def call(self, inputs, mask, training): | |
attention = self.multi_head_attention(inputs, | |
inputs, | |
inputs, | |
mask) | |
attention = self.dropout_1(attention, training) | |
attention = self.norm_1(attention + inputs) | |
outputs = self.Dense_1(attention) | |
outputs = self.Dense_2(outputs) | |
outputs = self.dropout_2(outputs, training) | |
outputs = self.norm_2(outputs + attention) | |
return outputs | |
class Encoder(Layer): | |
def __init__(self, nb_layers, FFN_units, | |
nb_proj, dropout_rate, | |
vocab_size, d_model, | |
name = "Encoder"): | |
super(Encoder, self).__init__(name = name) | |
self.nb_layers = nb_layers | |
self.d_model = d_model | |
self.embedding = Embedding(vocab_size, d_model) | |
self.pos_encoder = PositionalEncoder() | |
self.dropout = Dropout(rate = dropout_rate) | |
self.enc_layers = [EncoderLayer(FFN_units, | |
nb_proj, | |
dropout_rate) | |
for _ in range(nb_layers)] | |
def call(self, inputs, mask, training): | |
outputs = self.embedding(inputs) | |
outputs *= tf.math.sqrt(tf.cast(self.d_model, tf.float32)) | |
outputs = self.pos_encoder(outputs) | |
outputs = self.dropout(outputs, training) | |
for i in range(self.nb_layers): | |
outputs = self.enc_layers[i](outputs, mask, training) | |
return outputs | |
class Transformer(Model): | |
def __init__(self, | |
vocab_size_enc, | |
vocab_size_dec, | |
d_model, | |
nb_layers, | |
FFN_units, | |
nb_proj, | |
dropout_rate, | |
name = "Transformer"): | |
super(Transformer, self).__init__(name = name) | |
self.encoder = Encoder(nb_layers, | |
FFN_units, | |
nb_proj, | |
dropout_rate, | |
vocab_size_enc, | |
d_model) | |
self.Flatten = Flatten() | |
self.Last_Dense = Dense(units = vocab_size_dec, activation = "sigmoid", name = "Linear_Output") | |
def create_padding_mask(self, seq): # seq: (batch_size, seq_length) | |
mask = tf.cast(tf.equal(seq, 0), dtype = tf.float32) | |
return mask[:, tf.newaxis, tf.newaxis, :] | |
def create_look_ahead_mask(self, seq): | |
seq_len = tf.shape(seq)[1] | |
look_ahead_mask = 1 - tf.linalg.band_part(tf.ones(shape = (seq_len, seq_len)), -1, 0) | |
return look_ahead_mask | |
def call(self, enc_inputs, training): | |
enc_mask = self.create_padding_mask(enc_inputs) | |
enc_outputs = self.encoder(enc_inputs, enc_mask, training) | |
enc_outputs = self.Flatten(enc_outputs) | |
outputs = self.Last_Dense(enc_outputs) | |
return outputs |