Positional Encodings in Transformers
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Questions and Answers

What role do positional encodings play in transformers?

  • They enhance the performance of pooling layers.
  • They capture the sequential order of words. (correct)
  • They help to initialize model weights.
  • They reduce the size of the model.

Absolute positional embeddings impose a limit on the maximum input size.

True (A)

Name one type of positional embeddings used in the original transformer architecture.

Sinusoidal Positional Embeddings

What type of positional encoding does T5 utilize?

<p>Rotary Positional Embeddings (RoPE) (B)</p> Signup and view all the answers

The ____________ encodings were proposed to use pairwise distances as a way of creating positional encodings.

<p>Relative Positional</p> Signup and view all the answers

Match the following types of positional embeddings with their characteristics:

<p>Absolute Positional Embeddings = Learned by the model, limited maximum input size Sinusoidal Positional Embeddings = Constructed using sine and cosine functions, not learned Relative Positional Encodings = Use pairwise distances for positional representation</p> Signup and view all the answers

ALiBi involves a constant positional bias that is learned by the network.

<p>False (B)</p> Signup and view all the answers

What is a limitation of sinusoidal positional embeddings?

<p>They can result in inadequate representation of long-range dependencies. (A)</p> Signup and view all the answers

Name one of the primary models that utilize Rotary Positional Embeddings.

<p>Llama</p> Signup and view all the answers

RoPE-scaling allows longer sequences to be processed with ______ fine-tuning.

<p>minimal</p> Signup and view all the answers

Token embeddings and positional embeddings are learned using different methodologies.

<p>False (B)</p> Signup and view all the answers

Match the following types of positional encoding methods with their characteristics:

<p>RoPE = Utilizes rotation matrices for positional information ALiBi = Adds a constant bias to attention scores T5 = Introduced a simplified method for pairwise distances Linear Scaling = Adjusts rotation for longer sequences</p> Signup and view all the answers

Which models used absolute positional embeddings?

<p>BERT and GPT-2</p> Signup and view all the answers

Which of the following statements about RoPE is correct?

<p>RoPE modifies Q and K vectors with rotation matrices. (A)</p> Signup and view all the answers

The positional information in modern encodings is added to the token embeddings.

<p>False (B)</p> Signup and view all the answers

What is the main trend in the new approaches to positional encoding?

<p>Embedding positional information in Query and Key vectors</p> Signup and view all the answers

Flashcards

Positional Embeddings in Transformers

In the original Transformer, positional encodings are vectors added to input and output embeddings. They help the model understand the order of words in a sequence.

Absolute Positional Embeddings

A type of positional embedding where each possible word position is represented by a unique vector. The model learns these vectors during training.

Maximum Input Size Limit in Absolute Positional Embeddings

A limitation of absolute positional embedding. The model can only handle a maximum input size that is defined by the size of the positional embedding table.

Sinusoidal Positional Embeddings

A type of positional encoding that uses sine and cosine functions to represent positions. They are not learned by the model, but are calculated based on the position.

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Limitations of Sinusoidal Positional Embeddings

Sinusoidal positional encodings have issues representing long sequences effectively. The frequency of the waves becomes very high, leading to inadequate capture of long-range dependencies and fine-grained positional information.

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Relative Positional Embeddings

A type of positional encoding that uses pairwise distances between words to represent their relative positions. It focuses on the relationships between words rather than absolute positions.

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Advantages of Relative Positional Embeddings

Relative positional encodings offer a way to deal with longer input sequences compared to absolute or sinusoidal positional embeddings, as they are not limited by a fixed-size table.

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Usage of Positional Embedding Types

The original Transformer architecture uses sinusoidal positional embeddings, while models like BERT and GPT-2 use absolute positional embeddings.

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Relative Positional Encoding

A type of positional encoding where the relative distance between tokens is encoded directly into the query (Q) and key (K) vectors used for attention.

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Rotary Positional Embeddings (RoPE)

A method for implementing relative positional encoding that uses rotation matrices to modify the Q and K vectors.

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RoPE-scaling

A technique for extending RoPE's capability to handle longer sequences by scaling the rotation factor.

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Attention with Linear Biases (ALiBi)

A method for relative positional encoding that adds a linear bias to the attention scores based on the distance between tokens.

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m (in ALiBi)

A scalar value that determines the strength of the linear bias in ALiBi.

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Positional Bias (ALiBi)

The constant positional bias added to the scaled dot-product attention in ALiBi.

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Relative Positional Encoding

Both RoPE and ALiBi are examples of this type of positional encoding.

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Generalization to Unseen Lengths

A significant advantage of relative positional encodings over traditional methods.

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Study Notes

Positional Encodings in Transformers

  • Positional encodings are crucial for transformers to understand the order of words/tokens in text.
  • They enable transformers to capture sequential relationships.
  • Original methods have limitations on maximum input sequence lengths.

Types of Positional Embeddings

Absolute Positional Embeddings

  • Learned embeddings, similar to token embeddings.
  • Model learns a separate embedding table for each possible position.
  • Limited by a fixed maximum input size.
  • Used in BERT and GPT-2.

Sinusoidal Positional Embeddings

  • Pre-computed, not learned by the model.
  • Use sine and cosine functions to generate positional embeddings.
  • Can have difficulties with long sequences as frequencies become too high.
  • Initially used in the original transformer architecture.

Relative Positional Encodings

  • Encode relative distances between tokens rather than absolute positions.
  • Generalized to indefinite sequence lengths.
  • T5 utilized a simplified relative distance calculation.
  • Commonly used implementations are RoPE and ALiBi.
  • Embed positional information directly into Q and K vectors for attention.

Rotary Positional Embeddings (RoPE)

  • Relative positional encoding method.
  • Does not add extra trainable parameters.
  • Modifies Q and K vectors using pre-computed rotation matrices.
  • Can handle longer sequences with RoPE-scaling.
  • Scaled rotation (e.g., mθ/N) allows for longer inputs.

Attention with Linear Biases (ALiBi)

  • Biases query-key attention scores based on distance.
  • Simple modification to scaled dot-product attention with a fixed positional bias.
  • Doesn't require learned parameters for the bias, not explicitly learned.
  • Used by BLOOM, BloombergGPT, and MPT.

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Description

This quiz covers the critical concept of positional encodings in transformer models, essential for maintaining the sequence of words or tokens in text processing. It explores various types including absolute, sinusoidal, and relative positional embeddings, detailing their advantages and limitations in handling input length. Test your understanding of these fundamental components in transformer architecture.

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