modeling4.py

import tensorflow as tf
from tensorflow.keras import layers, activations, initializers

class MiniSunConfig:
    def __init__(self, vocab_size=30522, max_position_embeddings=1024, hidden_size=512,
                 num_attention_heads=8, intermediate_size=2048, num_hidden_layers=8,
                 dropout_rate=0.1, weight_decay=0.01, learning_rate=1e-4, total_steps=2500, warmup_steps=0.2):
        self.vocab_size = vocab_size
        self.max_position_embeddings = max_position_embeddings
        self.hidden_size = hidden_size
        self.num_attention_heads = num_attention_heads
        self.intermediate_size = intermediate_size
        self.num_hidden_layers = num_hidden_layers
        self.dropout_rate = dropout_rate
        self.weight_decay = weight_decay
        self.learning_rate = learning_rate
        self.total_steps = total_steps
        self.warmup_steps = warmup_steps

@tf.keras.utils.register_keras_serializable()
class MiniSunModel(tf.keras.Model):
    def __init__(self, config):
        super(MiniSunModel, self).__init__()
        self.config = config

        # Embedding layers for token and position
        self.token_embedding = layers.Embedding(config.vocab_size, config.hidden_size)
        self.position_embedding = layers.Embedding(config.max_position_embeddings, config.hidden_size)

        # Initialize an empty list for decoder blocks
        self.decoder_blocks = []

        # Final normalization and head
        self.layer_norm = layers.LayerNormalization(epsilon=1e-6)
        self.lm_head = layers.Dense(config.vocab_size, kernel_initializer=initializers.he_normal())

    def build(self, input_shape):
        # Create transformer decoder blocks based on the model configuration
        self.decoder_blocks = [self._build_decoder_block() for _ in range(self.config.num_hidden_layers)]
        # Call the superclass's build method
        super(MiniSunModel, self).build(input_shape)

    def _build_decoder_block(self):
        # Decoder block consisting of multi-head attention and feed-forward layers
        return [
            layers.MultiHeadAttention(num_heads=self.config.num_attention_heads, key_dim=self.config.hidden_size,
                                      kernel_initializer=initializers.he_normal()),
            layers.LayerNormalization(epsilon=1e-6),
            layers.Dense(self.config.intermediate_size, activation=activations.elu,
                         kernel_initializer=initializers.he_normal()),
            layers.Dense(self.config.hidden_size, kernel_initializer=initializers.he_normal()),
            layers.Dropout(self.config.dropout_rate)
        ]

    def call(self, inputs, attention_mask=None, training=False):
        input_ids = inputs['input_ids']
        position_ids = tf.range(start=0, limit=tf.shape(input_ids)[-1], delta=1)

        # Token and position embeddings
        embeddings = self.token_embedding(input_ids) + self.position_embedding(position_ids)

        # Adjust attention mask to correct shape [batch_size, 1, 1, seq_len]
        if attention_mask is not None:
            attention_mask = tf.cast(attention_mask[:, tf.newaxis, tf.newaxis, :], dtype=tf.float32)

        # Apply decoder blocks
        hidden_states = embeddings
        for mha, norm, ffn1, ffn2, dropout in self.decoder_blocks:
            attn_output = mha(hidden_states, hidden_states, attention_mask=attention_mask, training=training)
            attn_output = dropout(attn_output, training=training)
            hidden_states = norm(attn_output + hidden_states)  # Add & Norm

            # Feed-forward layers
            ffn_output = ffn1(hidden_states)
            ffn_output = ffn2(ffn_output)
            ffn_output = dropout(ffn_output, training=training)
            hidden_states = norm(ffn_output + hidden_states)  # Add & Norm

        # Final layer normalization
        hidden_states = self.layer_norm(hidden_states)

        # LM Head for token generation
        logits = self.lm_head(hidden_states)
        return logits

    def get_config(self):
        # Return the configuration of the model
        return {
            'config': self.config.__dict__
        }

    @classmethod
    def from_config(cls, config):
        # Create an instance of the model from the config
        return cls(MiniSunConfig(**config['config']))
    
    def compute_loss(self, labels, logits):
        """Computes the loss between labels and logits."""
        if labels is None or logits is None:
            raise ValueError("Labels and logits cannot be None.")
        return tf.keras.losses.sparse_categorical_crossentropy(labels, logits, from_logits=True)

    def train_step(self, data):
        inputs, labels = data
        input_ids = inputs['input_ids']
        attention_mask = inputs['attention_mask']

        with tf.GradientTape() as tape:
            logits = self(inputs, training=True)
            loss = self.compute_loss(labels, logits)

        gradients = tape.gradient(loss, self.trainable_variables)
        self.optimizer.apply_gradients(zip(gradients, self.trainable_variables))

        logits_for_metrics = tf.argmax(logits, axis=-1)
        logits_for_metrics = tf.reshape(logits_for_metrics, [-1])
        labels_for_metrics = tf.reshape(labels, [-1])

        for metric in self.metrics:
            metric.update_state(labels_for_metrics, logits_for_metrics) 

        return {m.name: m.result() for m in self.metrics}

def create_model(config):
    model = MiniSunModel(config)

    # Optimizer with weight decay
    optimizer = tf.keras.optimizers.AdamW(learning_rate=config.learning_rate, weight_decay=config.weight_decay)

    model.compile(
        optimizer=optimizer,
        loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True),
        metrics=['accuracy']
    )
    return model

def cosine_annealing_with_warmup(step, config):
    """Learning rate schedule with warm-up and cosine annealing."""
    warmup_steps = int(config.total_steps * config.warmup_steps)
    if step < warmup_steps:
        return config.learning_rate * (step / warmup_steps)
    else:
        cos_step = step - warmup_steps
        total_cos_steps = config.total_steps - warmup_steps
        return 0.5 * config.learning_rate * (1 + tf.cos(tf.constant(np.pi) * cos_step / total_cos_steps))

def cosine_annealing_with_restarts(step, config, restart_period, cycle_num):
    """Learning rate schedule with warm-up and cosine annealing with restarts."""
    warmup_steps = int(config.total_steps * config.warmup_steps)
    
    current_cycle = step // restart_period
    effective_step = step % restart_period

    if effective_step < warmup_steps:
        return config.learning_rate * (effective_step / warmup_steps)
    else:
        cos_step = effective_step - warmup_steps
        total_cos_steps = restart_period - warmup_steps
        return 0.5 * config.learning_rate * (1 + tf.cos(tf.constant(np.pi) * cos_step / total_cos_steps))

# Configuration
config = MiniSunConfig()

# Initialize model with He initialization
model = create_model(config)

# Create a LearningRateScheduler callback
lr_scheduler = tf.keras.callbacks.LearningRateScheduler(lambda step: cosine_annealing_with_warmup(step, config))
# lr_scheduler_with_restarts = tf.keras.callbacks.LearningRateScheduler(lambda step: cosine_annealing_with_restarts(step, config, restart_period=1000, cycle_num=1))