Update README.md
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README.md
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@@ -315,104 +315,6 @@ After each epoch, the model is evaluated on the validation set, computing the av
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### Checkpoints
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At the end of each epoch, the model saves checkpoints of all components, enabling easy resumption or further fine-tuning as needed.
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## Language Model Architecture
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### Transformer Architecture
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The Transformer architecture is foundational to the LightBulb model, facilitating efficient sequence processing through self-attention mechanisms and feedforward networks enhanced by Mixture of Experts (MoE).
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#### TransformerBlock
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Each `TransformerBlock` consists of the following components:
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1. **Self-Attention (`self_attention`)**
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2. **Layer Normalization (`norm1`)**
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3. **Cross-Attention (`cross_attention`)**
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4. **Layer Normalization (`norm2`)**
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5. **Mixture of Experts (`moe`)**
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6. **Layer Normalization (`norm3`)**
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**Mathematical Operations:**
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1. **Self-Attention:**
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\[
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\text{Attn}_{\text{self}} = \text{SelfAttention}(Q, K, V) = \text{softmax}\left(\frac{QK^\top}{\sqrt{d_k}}\right)V
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\]
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2. **Residual Connection and Layer Norm:**
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\[
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x = \text{LayerNorm}(x + \text{Attn}_{\text{self}})
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\]
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3. **Cross-Attention (if applicable):**
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\[
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\text{Attn}_{\text{cross}} = \text{CrossAttention}(Q, K_{\text{enc}}, V_{\text{enc}}) = \text{softmax}\left(\frac{QK_{\text{enc}}^\top}{\sqrt{d_k}}\right)V_{\text{enc}}
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\]
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\[
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x = \text{LayerNorm}(x + \text{Attn}_{\text{cross}})
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\]
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4. **Mixture of Experts:**
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\[
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\text{MoE}_{\text{output}} = \sum_{i=1}^k g_i(x) \cdot \text{Expert}_i(x)
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\]
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5. **Residual Connection and Layer Norm:**
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\[
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x = \text{LayerNorm}(x + \text{MoE}_{\text{output}})
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\]
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**Key Parameters:**
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- \( d_{\text{model}} \): Dimensionality of the model embeddings.
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- \( d_k \): Dimensionality of the key vectors in attention.
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- \( \text{num\_heads} \): Number of attention heads.
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- \( \text{num\_experts} \): Number of experts in the MoE layer.
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- \( \text{top\_k} \): Number of top experts to activate in MoE.
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- \( \text{dropout} \): Dropout rate for regularization.
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#### Transformer
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The `Transformer` class orchestrates multiple `TransformerBlock` instances within encoder and decoder stacks.
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**Components:**
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1. **Embedding Layer:**
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\[
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E = \text{Embedding}(input\_ids) \times \sqrt{d_{\text{model}}}
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\]
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2. **Rotary Positional Encoding (`rotary_positional_encoding`):**
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- Injects positional information by rotating the embeddings based on token positions.
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3. **Encoder and Decoder Layers:**
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- Multiple `TransformerBlock` instances processing the embedded inputs.
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4. **Output Layer:**
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\[
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\text{Output} = \text{Linear}(d_{\text{model}}, \text{output\_dim})(\text{Decoder Output})
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\]
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5. **Beam Search with Multi-Token Prediction (`generate_with_beam_search`):**
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- Generates sequences by predicting multiple tokens at each step, maintaining a beam of top candidates.
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**Forward Pass:**
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\[
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\begin{align*}
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\text{Encoder:} & \quad X_{\text{enc}} = \text{Embedding}(src) \times \sqrt{d_{\text{model}}} \\
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& \quad X_{\text{enc}} = \text{RotaryPositionalEncoding}(X_{\text{enc}}) \\
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& \quad X_{\text{enc}} = \text{EncoderLayers}(X_{\text{enc}}) \\
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\\
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\text{Decoder:} & \quad X_{\text{dec}} = \text{Embedding}(tgt) \times \sqrt{d_{\text{model}}} \\
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& \quad X_{\text{dec}} = \text{RotaryPositionalEncoding}(X_{\text{dec}}) \\
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& \quad X_{\text{dec}} = \text{DecoderLayers}(X_{\text{dec}}, X_{\text{enc}}) \\
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\\
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\text{Output:} & \quad \text{output} = \text{Linear}(X_{\text{dec}})
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\end{align*}
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\]
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---
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### World Model Components
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Transforms the transformer's output embeddings into a compact state representation suitable for modeling and prediction tasks.
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**Mathematical Operation:**
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\[
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\text{State} = \text{LayerNorm}\left(\text{Linear}(d_{\text{model}} \rightarrow d_{\text{state}})\left(\text{Linear}(vocab\_dim \rightarrow d_{\text{model}})(\text{Transformer Output})\right)\right)
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\]
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**Explanation:**
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Sequential linear transformations project high-dimensional embeddings into a lower-dimensional state space, followed by layer normalization for stability.
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Models how the state evolves in response to actions (thoughts) taken by the model.
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**Mathematical Operation:**
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\[
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\text{Next State} = \text{DynamicsNetwork}(\text{Current State}, \text{Action Embedding})
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\]
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**Explanation:**
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Predicts the subsequent state by combining the current state representation with an encoded action, effectively simulating the consequences of actions within the Tree of Thought.
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Predicts policy logits (action probabilities) and value estimates (state evaluations) based on the current state.
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**Mathematical Operation:**
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\[
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(\text{Policy Logits}, \text{Value Estimate}) = \text{PredictionNetwork}(\text{State})
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\]
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**Explanation:**
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- **Policy Logits:** Used to derive action probabilities via softmax.
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- **Value Estimate:** Represents the expected reward or quality of the current state.
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Encodes discrete actions (thoughts) into continuous embeddings compatible with the DynamicsNetwork.
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**Mathematical Operation:**
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\[
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\text{Action Embedding} = \text{ActionEncoder}(\text{Action Index})
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\]
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**Explanation:**
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Converts action indices into dense vector representations, facilitating their integration into state transition modeling.
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**Mathematical Representation:**
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Each `ThoughtNode` can be represented as a tree node in a directed graph:
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\[
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\text{ThoughtNode} = (\text{name}, \{\text{children}\})
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\]
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#### State
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**Function:**
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- `thought_node`: Reference to the current `ThoughtNode` in the Tree of Thought.
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**Action Application (`apply_action`):**
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\[
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\text{Next State} = \text{DynamicsNetwork}(\text{Current State}, \text{Action Embedding})
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\]
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\[
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\text{New Representation} = \text{Concat}(\text{Current Representation}, \text{Next State} \rightarrow \text{unsqueeze}(1))
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\]
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**Procedure:**
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1. **Action Encoding:**
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\[
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\text{Action Index} = \text{Index of Action}
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\]
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\[
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\text{Action Embedding} = \text{ActionEncoder}(\text{Action Index})
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\]
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2. **State Extraction:**
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\[
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\text{Current State} = \text{representation}[:, -1, :]
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\]
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3. **State Transition:**
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\[
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\text{Next State Representation} = \text{DynamicsNetwork}(\text{Current State}, \text{Action Embedding})
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\]
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4. **Representation Update:**
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\[
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\text{New Representation} = \text{Concat}(\text{representation}, \text{Next State Representation} \times \text{unsqueeze}(1))
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\]
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5. **Thought Node Update:**
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- Navigate to the child `ThoughtNode` corresponding to the applied action.
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**Mathematical Representation:**
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Each `MCTSNode` can be considered as:
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\[
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\text{MCTSNode} = (\text{state}, \text{parent}, \text{action}, \{\text{children}\}, \text{visit\_count}, \text{value\_sum}, \text{prior}, \text{entropy}, \text{variance})
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\]
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#### MCTS Algorithm
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The `MCTS` class implements the Monte Carlo Tree Search algorithm tailored to the LightBulb model's architecture.
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- Add the candidate sequence to `all_candidates`.
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- **Beam Pruning:**
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- Sort all candidates based on a combined score:
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\[
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\text{Combined Score} = \text{Score} - 0.1 \times \text{Entropy} + 0.05 \times \text{Variance}
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\]
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- Retain the top `beam_size` candidates for the next iteration.
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4. **Result Extraction:**
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- After completing iterations, select the best action sequence from the final beam.
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- Calculate entropy and variance of the policy distribution.
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- Expand the node by creating child nodes based on the Tree of Thought and assign priors from policy probabilities.
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- **Mathematical Operations:**
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\[
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(\text{Policy Logits}, \text{Value Estimate}) = \text{PredictionNetwork}(\text{State})
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\]
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\[
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\text{Variance} = \text{Var}(P)
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\]
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4. **Backpropagation (`backpropagate`):**
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- **Function:** Updates the `visit_count` and `value_sum` for nodes along the path from the evaluated node back to the root.
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- **Procedure:**
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\[
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\text{For each node in the path:} \\
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\quad \text{node.visit\_count} \mathrel{+}= 1 \\
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\quad \text{node.value\_sum} \mathrel{+}= \text{Value Estimate}
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\]
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5. **Upper Confidence Bound (UCB) Score (`ucb_score`):**
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- **Function:** Balances exploration of less-visited nodes and exploitation of high-value nodes.
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- **Mathematical Operation:**
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\[
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\text{UCB Score} = \text{Average Value} + \text{Exploration Term} + \text{Entropy Term} + \text{Variance Term}
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\]
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\[
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\text{Variance Term} = 0.05 \times \text{variance}
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\]
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6. **Best Action Sequence Extraction (`best_action_sequence`):**
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- **Function:** Extracts the most promising action sequence from the MCTS tree after all iterations.
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- **Procedure:**
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---
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### Mixture of Experts (MoE)
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\[
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\text{MoE}(x) = \sum_{i=1}^k g_i(x) \cdot \text{Expert}_i(x)
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\]
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Where:
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- \( g_i(x) \): Gating weights ensuring sparsity (only top-k experts are active).
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- \( \text{Expert}_i(x) \): Outputs from the expert networks.
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- \( k \): Number of top experts to activate.
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**Explanation:**
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- For each input, only the top-k experts (based on gating scores) process the data.
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- Reduces computational load while maintaining high capacity.
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### Beam Search with Multi-Token Prediction
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**Purpose:** Efficiently explores multiple possible token sequences to generate coherent and diverse outputs by predicting multiple tokens at each step.
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**Procedure:**
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1. **Beam Initialization:**
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- Start with a beam containing the start-of-sequence (BOS) token.
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\[
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\text{beam} = \left\{ \left( \text{seq} = [\text{BOS}], \text{score} = 0, \text{cum\_entropy} = 0, \text{cum\_variance} = 0 \right) \right\}
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\]
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2. **Iterative Expansion:**
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- For each sequence in the beam:
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- Predict the next
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- Calculate their probabilities.
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- Select top-k token sequences based on cumulative scores.
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- Continue until the maximum length is reached or all sequences end with the end-of-sequence (EOS) token.
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**Mathematical Operations:**
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\[
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\text{Score} = \sum_{t=1}^{n} \log P(\text{token}_t | \text{tokens}_{<t})
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\]
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\[
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\text{Variance} = \text{Var}(P)
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\]
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Where \( P \) is the probability distribution over the vocabulary.
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### Upper Confidence Bound (UCB) in MCTS
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### Checkpoints
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At the end of each epoch, the model saves checkpoints of all components, enabling easy resumption or further fine-tuning as needed.
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---
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### World Model Components
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Transforms the transformer's output embeddings into a compact state representation suitable for modeling and prediction tasks.
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**Mathematical Operation:**
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+
```
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\[
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\text{State} = \text{LayerNorm}\left(\text{Linear}(d_{\text{model}} \rightarrow d_{\text{state}})\left(\text{Linear}(vocab\_dim \rightarrow d_{\text{model}})(\text{Transformer Output})\right)\right)
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\]
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```
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**Explanation:**
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Sequential linear transformations project high-dimensional embeddings into a lower-dimensional state space, followed by layer normalization for stability.
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Models how the state evolves in response to actions (thoughts) taken by the model.
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**Mathematical Operation:**
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+
```
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\[
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\text{Next State} = \text{DynamicsNetwork}(\text{Current State}, \text{Action Embedding})
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\]
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+
```
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**Explanation:**
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Predicts the subsequent state by combining the current state representation with an encoded action, effectively simulating the consequences of actions within the Tree of Thought.
|
|
|
|
| 356 |
Predicts policy logits (action probabilities) and value estimates (state evaluations) based on the current state.
|
| 357 |
|
| 358 |
**Mathematical Operation:**
|
| 359 |
+
```
|
| 360 |
\[
|
| 361 |
(\text{Policy Logits}, \text{Value Estimate}) = \text{PredictionNetwork}(\text{State})
|
| 362 |
\]
|
| 363 |
+
```
|
| 364 |
**Explanation:**
|
| 365 |
- **Policy Logits:** Used to derive action probabilities via softmax.
|
| 366 |
- **Value Estimate:** Represents the expected reward or quality of the current state.
|
|
|
|
| 371 |
Encodes discrete actions (thoughts) into continuous embeddings compatible with the DynamicsNetwork.
|
| 372 |
|
| 373 |
**Mathematical Operation:**
|
| 374 |
+
```
|
| 375 |
\[
|
| 376 |
\text{Action Embedding} = \text{ActionEncoder}(\text{Action Index})
|
| 377 |
\]
|
| 378 |
+
```
|
| 379 |
**Explanation:**
|
| 380 |
Converts action indices into dense vector representations, facilitating their integration into state transition modeling.
|
| 381 |
|
|
|
|
| 399 |
**Mathematical Representation:**
|
| 400 |
|
| 401 |
Each `ThoughtNode` can be represented as a tree node in a directed graph:
|
| 402 |
+
```
|
| 403 |
\[
|
| 404 |
\text{ThoughtNode} = (\text{name}, \{\text{children}\})
|
| 405 |
\]
|
| 406 |
+
```
|
| 407 |
#### State
|
| 408 |
|
| 409 |
**Function:**
|
|
|
|
| 417 |
- `thought_node`: Reference to the current `ThoughtNode` in the Tree of Thought.
|
| 418 |
|
| 419 |
**Action Application (`apply_action`):**
|
| 420 |
+
```
|
| 421 |
\[
|
| 422 |
\text{Next State} = \text{DynamicsNetwork}(\text{Current State}, \text{Action Embedding})
|
| 423 |
\]
|
| 424 |
\[
|
| 425 |
\text{New Representation} = \text{Concat}(\text{Current Representation}, \text{Next State} \rightarrow \text{unsqueeze}(1))
|
| 426 |
\]
|
| 427 |
+
```
|
| 428 |
**Procedure:**
|
| 429 |
|
| 430 |
1. **Action Encoding:**
|
| 431 |
+
|
| 432 |
+
```
|
| 433 |
\[
|
| 434 |
\text{Action Index} = \text{Index of Action}
|
| 435 |
\]
|
| 436 |
\[
|
| 437 |
\text{Action Embedding} = \text{ActionEncoder}(\text{Action Index})
|
| 438 |
\]
|
| 439 |
+
```
|
| 440 |
2. **State Extraction:**
|
| 441 |
+
|
| 442 |
+
```
|
| 443 |
\[
|
| 444 |
\text{Current State} = \text{representation}[:, -1, :]
|
| 445 |
\]
|
| 446 |
+
```
|
| 447 |
3. **State Transition:**
|
| 448 |
+
|
| 449 |
+
```
|
| 450 |
\[
|
| 451 |
\text{Next State Representation} = \text{DynamicsNetwork}(\text{Current State}, \text{Action Embedding})
|
| 452 |
\]
|
| 453 |
+
```
|
| 454 |
4. **Representation Update:**
|
| 455 |
+
|
| 456 |
+
```
|
| 457 |
\[
|
| 458 |
\text{New Representation} = \text{Concat}(\text{representation}, \text{Next State Representation} \times \text{unsqueeze}(1))
|
| 459 |
\]
|
| 460 |
+
```
|
| 461 |
5. **Thought Node Update:**
|
| 462 |
- Navigate to the child `ThoughtNode` corresponding to the applied action.
|
| 463 |
|
|
|
|
| 487 |
**Mathematical Representation:**
|
| 488 |
|
| 489 |
Each `MCTSNode` can be considered as:
|
| 490 |
+
```
|
| 491 |
\[
|
| 492 |
\text{MCTSNode} = (\text{state}, \text{parent}, \text{action}, \{\text{children}\}, \text{visit\_count}, \text{value\_sum}, \text{prior}, \text{entropy}, \text{variance})
|
| 493 |
\]
|
| 494 |
+
```
|
| 495 |
#### MCTS Algorithm
|
| 496 |
|
| 497 |
The `MCTS` class implements the Monte Carlo Tree Search algorithm tailored to the LightBulb model's architecture.
|
|
|
|
| 521 |
- Add the candidate sequence to `all_candidates`.
|
| 522 |
- **Beam Pruning:**
|
| 523 |
- Sort all candidates based on a combined score:
|
| 524 |
+
```
|
| 525 |
\[
|
| 526 |
\text{Combined Score} = \text{Score} - 0.1 \times \text{Entropy} + 0.05 \times \text{Variance}
|
| 527 |
\]
|
| 528 |
+
```
|
| 529 |
- Retain the top `beam_size` candidates for the next iteration.
|
| 530 |
4. **Result Extraction:**
|
| 531 |
- After completing iterations, select the best action sequence from the final beam.
|
|
|
|
| 539 |
- Calculate entropy and variance of the policy distribution.
|
| 540 |
- Expand the node by creating child nodes based on the Tree of Thought and assign priors from policy probabilities.
|
| 541 |
- **Mathematical Operations:**
|
| 542 |
+
```
|
| 543 |
\[
|
| 544 |
(\text{Policy Logits}, \text{Value Estimate}) = \text{PredictionNetwork}(\text{State})
|
| 545 |
\]
|
|
|
|
| 552 |
\[
|
| 553 |
\text{Variance} = \text{Var}(P)
|
| 554 |
\]
|
| 555 |
+
```
|
| 556 |
4. **Backpropagation (`backpropagate`):**
|
| 557 |
- **Function:** Updates the `visit_count` and `value_sum` for nodes along the path from the evaluated node back to the root.
|
| 558 |
- **Procedure:**
|
| 559 |
+
```
|
| 560 |
\[
|
| 561 |
\text{For each node in the path:} \\
|
| 562 |
\quad \text{node.visit\_count} \mathrel{+}= 1 \\
|
| 563 |
\quad \text{node.value\_sum} \mathrel{+}= \text{Value Estimate}
|
| 564 |
\]
|
| 565 |
+
```
|
| 566 |
5. **Upper Confidence Bound (UCB) Score (`ucb_score`):**
|
| 567 |
- **Function:** Balances exploration of less-visited nodes and exploitation of high-value nodes.
|
| 568 |
- **Mathematical Operation:**
|
| 569 |
+
|
| 570 |
+
```
|
| 571 |
\[
|
| 572 |
\text{UCB Score} = \text{Average Value} + \text{Exploration Term} + \text{Entropy Term} + \text{Variance Term}
|
| 573 |
\]
|
|
|
|
| 584 |
\[
|
| 585 |
\text{Variance Term} = 0.05 \times \text{variance}
|
| 586 |
\]
|
| 587 |
+
```
|
| 588 |
6. **Best Action Sequence Extraction (`best_action_sequence`):**
|
| 589 |
- **Function:** Extracts the most promising action sequence from the MCTS tree after all iterations.
|
| 590 |
- **Procedure:**
|
|
|
|
| 594 |
|
| 595 |
---
|
| 596 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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|
|
|
|
|
|
|
|
|
|
| 597 |
### Beam Search with Multi-Token Prediction
|
| 598 |
|
| 599 |
**Purpose:** Efficiently explores multiple possible token sequences to generate coherent and diverse outputs by predicting multiple tokens at each step.
|
|
|
|
| 601 |
**Procedure:**
|
| 602 |
|
| 603 |
1. **Beam Initialization:**
|
| 604 |
+
|
| 605 |
+
```
|
| 606 |
- Start with a beam containing the start-of-sequence (BOS) token.
|
| 607 |
\[
|
| 608 |
\text{beam} = \left\{ \left( \text{seq} = [\text{BOS}], \text{score} = 0, \text{cum\_entropy} = 0, \text{cum\_variance} = 0 \right) \right\}
|
| 609 |
\]
|
| 610 |
+
```
|
| 611 |
2. **Iterative Expansion:**
|
| 612 |
+
- For each iteration up to
|
| 613 |
+
```
|
| 614 |
+
\( \frac{\text{max\_length}}{n\_tokens\_predict} \)
|
| 615 |
+
```
|
| 616 |
+
:
|
| 617 |
- For each sequence in the beam:
|
| 618 |
+
- Predict the next:
|
| 619 |
+
```
|
| 620 |
+
\( n\_tokens\_predict \)
|
| 621 |
+
|
| 622 |
+
```
|
| 623 |
+
tokens.
|
| 624 |
- Calculate their probabilities.
|
| 625 |
- Select top-k token sequences based on cumulative scores.
|
| 626 |
|
|
|
|
| 631 |
- Continue until the maximum length is reached or all sequences end with the end-of-sequence (EOS) token.
|
| 632 |
|
| 633 |
**Mathematical Operations:**
|
| 634 |
+
```
|
| 635 |
\[
|
| 636 |
\text{Score} = \sum_{t=1}^{n} \log P(\text{token}_t | \text{tokens}_{<t})
|
| 637 |
\]
|
|
|
|
| 641 |
\[
|
| 642 |
\text{Variance} = \text{Var}(P)
|
| 643 |
\]
|
| 644 |
+
```
|
| 645 |
Where \( P \) is the probability distribution over the vocabulary.
|
| 646 |
|
| 647 |
### Upper Confidence Bound (UCB) in MCTS
|