Advanced Transformer Architecture
Chapter 1: Revisiting Sequence Modeling Limitations
Sequential Computation in Recurrent Networks
The Vanishing and Exploding Gradient Problems
Long Short-Term Memory (LSTM) Gating Mechanisms
Gated Recurrent Units (GRUs) Architecture
Challenges with Long-Range Dependencies
Parallelization Constraints in Recurrent Models
Chapter 2: The Attention Mechanism: Core Concepts
Motivation: Overcoming Fixed-Length Context Vectors
General Framework: Query, Key, Value Abstraction
Mathematical Formulation of Dot-Product Attention
Scaled Dot-Product Attention
The Softmax Function for Attention Weights
Computational Aspects and Matrix Operations
Practice: Implementing Scaled Dot-Product Attention
Chapter 3: Multi-Head Self-Attention
Self-Attention: Queries, Keys, Values from the Same Source
Limitations of Single Attention Head
Introducing Multiple Attention Heads
Linear Projections for Q, K, V per Head
Parallel Attention Computations
Concatenation and Final Linear Projection
Analysis of What Different Heads Learn
Hands-on Practical: Building a Multi-Head Attention Layer
Chapter 4: Positional Encoding and Embedding Layer
The Need for Positional Information
Input Embedding Layer Transformation
Sinusoidal Positional Encoding: Formulation
Properties of Sinusoidal Encodings
Combining Embeddings and Positional Encodings
Alternative: Learned Positional Embeddings
Comparison: Sinusoidal vs. Learned Embeddings
Practice: Generating and Visualizing Positional Encodings
Chapter 5: Encoder and Decoder Stacks
Overall Transformer Architecture Overview
Encoder Layer Structure
Decoder Layer Structure
Masked Self-Attention in Decoders
Encoder-Decoder Cross-Attention
Position-wise Feed-Forward Networks (FFN)
Residual Connections (Add)
Layer Normalization (Norm)
Stacking Multiple Layers
Final Linear Layer and Softmax Output
Hands-on Practical: Constructing an Encoder Block
Chapter 6: Advanced Architectural Variants and Analysis
Computational Complexity of Self-Attention
Sparse Attention Mechanisms
Approximating Attention: Linear Transformers
Kernel-Based Attention Approximation (Performers)
Low-Rank Projection Methods (Linformer)
Transformer-XL: Segment-Level Recurrence
Relative Positional Encodings
Pre-Normalization vs Post-Normalization (Pre-LN vs Post-LN)
Scaling Laws for Neural Language Models
Parameter Efficiency and Sharing Techniques
Chapter 7: Implementation Details and Optimization
Choosing a Framework (PyTorch, TensorFlow, JAX)
Weight Initialization Strategies
Optimizers for Transformers (Adam, AdamW)
Learning Rate Scheduling (Warmup, Decay)
Regularization Techniques (Dropout, Label Smoothing)
Gradient Clipping
Mixed-Precision Training
Efficient Attention Implementations (FlashAttention)
Model Parallelism and Data Parallelism Strategies
Practice: Analyzing Attention Weight Distributions
Encoder and Decoder Stacks
Having established the principles of self-attention and positional encoding, we now focus on how these elements are integrated within the complete Transformer model. This chapter examines the architecture of the encoder and decoder stacks, which are the fundamental building blocks.
You will learn to:
- Identify the components of a standard Transformer encoder layer, including multi-head self-attention and position-wise feed-forward networks.
- Analyze the structure of a decoder layer, focusing on masked self-attention, encoder-decoder cross-attention, and feed-forward sub-layers.
- Understand the function of masked self-attention in preventing information flow from future tokens during sequence generation.
- Grasp how cross-attention allows the decoder to focus on relevant parts of the input sequence via the encoder's output.
- Recognize the role and implementation of residual connections (often denoted as Add) and layer normalization (Norm) in facilitating information propagation and stabilizing training within deep networks.
- Appreciate how stacking multiple identical layers forms the deep encoder and decoder structures.
- Trace the data flow from the input embeddings through the encoder and decoder stacks to the final output probabilities.
Sections
5.1 Overall Transformer Architecture Overview
5.2 Encoder Layer Structure
5.3 Decoder Layer Structure
5.4 Masked Self-Attention in Decoders
5.5 Encoder-Decoder Cross-Attention
5.6 Position-wise Feed-Forward Networks (FFN)
5.7 Residual Connections (Add)
5.8 Layer Normalization (Norm)
5.9 Stacking Multiple Layers
5.10 Final Linear Layer and Softmax Output
5.11 Hands-on Practical: Constructing an Encoder Block
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