Rotary Positional Embeddings: Combining Absolute and Relative
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- Опубліковано 4 чер 2024
- In this video, I explain RoPE - Rotary Positional Embeddings. Proposed in 2022, this innovation is swiftly making its way into prominent language models like Google's PaLM and Meta's LLaMa. I unpack the magic behind rotary embeddings and reveal how they combine the strengths of both absolute and relative positional encodings.
0:00 - Introduction
1:22 - Absolute positional embeddings
3:19 - Relative positional embeddings
5:51 - Rotary positional embeddings
7:56 - Matrix formulation
9:31 - Implementation
10:38 - Experiments and conclusion
References:
RoFormer: Enhanced Transformer with Rotary Position Embedding (main paper that proposes RoPE embeddings): arxiv.org/abs/2104.09864
EleutherAI blog post: blog.eleuther.ai/rotary-embed...
Blog posts by first author Jianlin Su (in Chinese): kexue.fm/archives/8130 and kexue.fm/archives/8265
Survey paper on positional embeddings: aclanthology.org/2022.cl-3.7/ - Наука та технологія
great explanation,really helped me!
Thanks for creating and sharing this vid! Still confused on the math stuff though. So I read through the paper and wrote down some notes:
The rotation matrix Rm rotates a query vector q of the mth token by mθ, while Rn rotates a key vector k of the nth token by nθ. For any rotation matrix or orthogonal matrix R, R^T = R^-1 holds. Thus Rm^T is Rm's inverse, that rotates q in another direction by -mθ. This means (q·Rm)^T·(k·Rn) can in total rotate q^T·k by (n-m)θ. This ultimately associates the knowledge extracted from the mth query and the nth key with their relative distance n - m, naturally and interpretably.
Genius
Amazing video, intuitive explanations with examples.
I've watched a few videos trying to wrap my head around this concept and yours is by far the best. Thanks!
Thank you so much. Your explanation is very clear and succinct.
your explanation is amazing. thank you for your work
Thanks for this overview!
Absolutely amazing explanation! Keep it up man
This is amazing, thank you
I just wrapped my mind around sinusoidal embeddings and came across rope and was really struggling to grasp it.
Definitely going to refer back to this video.
I love in depth NLP content like this.
Excellent video, thanks!
*Video Summary: Rotary Positional Embeddings: Combining Absolute and Relative*
- *Introduction*
- Discusses the importance of positional embeddings in Transformer models.
- *Absolute Positional Embeddings*
- Explains how absolute positional embeddings work.
- Highlights limitations like fixed sequence length and lack of relative context.
- *Relative Positional Embeddings*
- Introduces the concept of relative positional embeddings.
- Discusses the computational challenges and inefficiencies.
- *Rotary Positional Embeddings (RoPE)*
- Combines the advantages of both absolute and relative embeddings.
- Uses rotation to encode position, preserving relative distances.
- *Matrix Formulation*
- Explains the mathematical formulation behind RoPE.
- *Implementation*
- Shows how RoPE can be implemented efficiently in PyTorch.
- *Experiments and Conclusion*
- Shares results of experiments showing RoPE's effectiveness and efficiency compared to other methods.
The video provides a comprehensive overview of Rotary Positional Embeddings, a new method that combines the strengths of both absolute and relative positional embeddings. It delves into the mathematical details and practical implementation, concluding with experimental results that validate its effectiveness.
Really good introduction, thanks
OMG!! Very good teaching!!!
Good work, I look 'forward' to the ReRoPE video. 😎
Very clear~~thanks!
very good explanation.
You make it easy to learn even for a high school student
Gemini: The video is about a new method for positional embeddings in transformers called rotary positional embeddings.
The Transformer architecture is a neural network architecture commonly used for various natural language processing tasks. A key challenge for Transformer models is that they are invariant to the order of words by default. This means that the model would not be able to distinguish between a sentence and its scrambled version. To address this challenge, positional embeddings are added to the Transformer model. There are two main types of positional embeddings: absolute positional embeddings and relative positional embeddings.
Absolute positional embeddings assign a unique vector to each position in a sentence. This approach however, can not handle sentences longer than the training data. Relative positional embeddings, on the other hand, represent the relationship between two words. While this method can handle sentences of any length, it requires additional computations in the self-attention layer, making it less efficient.
Rotary positional embeddings address the limitations of both absolute and relative positional embeddings. The core idea is to rotate the word vector instead of adding a separate positional embedding vector. The amount of rotation is determined by the position of the word in the sentence. This way, rotary positional embeddings capture the absolute position of a word while also preserving the relative positions between words.
The video also mentions that rotary positional embeddings have been shown to improve the training speed of language models.░
thanks alot
I just smashed the like button.
Thanks for the in-depth explanation of RoPE. A couple of questions:
1. How is KV Cache used/built for RoPE case? RoPE is applied to q and K. Does this change anything in how K and V are cached?
2. Where can I find intuition behind why this RoPE works? I usually find it harder to jump into the mathematical equations directly to find the proof.
Yes, the KV cache can be used normally with RoPE, because the rotation is applied to a token depending on its position from the start of the sequence, and this does not change as more tokens are generated. I hope this video provides a good intuition of why this works!
Thanks for a great explanation! By the way, I was curious when I understood from the initial explanation and the rotational equations, consecutive pairs of coordinates seem to be rotated, as in (x_1, x_2) / (x_3, x_4) ... are each rotated. However from most of the implementations as suggested in the video, the codes pair up not by adjacent indices but with a window size of half the dimension, which would be (x_1, x_d//2+1) / (x_2, x_d//2+2) ... since the code states that we split the hdim by half and swap their order.. did I understand correctly or am I missing something?
You are correct. In many implementations, rather than rotating each pair of adjacent dimensions, they choose to split the entire vector in half and rotate the two halves. Ultimately, this does not matter because the dimensions of vectors are interchangeable and do not affect vector addition and multiplication. This is likely to be more efficient from an implementation standpoint and is equivalent to the original formula.
Great vid! Nice explanation! Question: why is it termed “rotary” and not “rotational” position embeddings?
It’s the name given in the paper. I think it’s quite catchy!
thank you for such a clear explaination, your explaination helped me to understand this concept,
rotary positional embedding is so elegant way to do positional embedding, and intuitively make sense to me,
curious how can this embedding technique works for vision transformer? anyone have experience?
Rotary embeddings may be applied to a vision transformer, just as they can be for any other transformer; I'm not aware of any reports that it improves performance in this case. It would be an interesting experiment, though!
Thanks @Bai for the great explanation.
I still have a question: Mathematically, why will the positional embedding of other positional embedding techniques (may be absolute?) change if adding more tokens to the sentence? Approximately, at minutes 7:00 of this video.
Thanks!
This is a property of most absolute positional embeddings, but generally not for relative positional embeddings. For example, T5's relative embeddings change at every step as different bias values need to be added to the attention matrix. Thus, rotary embeddings are the first to combine the benefits of both absolute and relative embeddings.
♥
great video but i have one question you are referring the eluther ai blog right? in that pytorch implementation instead of rotating every 2 elements in dim vector they rotated half vector like this ```def rotate_half(x):
x1, x2 = x.chunk(2, dim=-1)
return torch.cat((-x2, x1), dim=-1)``` but in the jax implementation they rotated every two elements any idea on this?
Yea that's possible, there are multiple ways to implement this but they should be logically equivalent.
Hi, thank you for this great video, but I wanted to ask how they should be logically equivalent, the values that were negated are not the same, so how they are logically eqivalent?@@EfficientNLP
Same question... Have you figured out the reason yet?😅@@hazemessamm
🎯 Key Takeaways for quick navigation:
00:14 🆕 *In 2022, a new architectural improvement called "Rotary Positional Embeddings" (ROPE) was proposed and adopted by various language models.*
03:27 🔄 *Relative positional embeddings represent token pairs' distances but face engineering challenges like slower processing for longer sequences.*
06:01 🔄 *Rotary positional embeddings propose rotating word vectors based on positions, combining advantages of both absolute and relative positional embeddings.*
08:04 🔢 *Rotary embeddings are implemented using rotation matrices for 2D cases and a more general approach for higher-dimensional vectors.*
10:48 ⚙️ *Experiments show that models using rotary positional embeddings train faster than those using sinusoidal embeddings and are relatively robust across various model architectures and training setups.*
Thanks for the good explanation!
How to actually make sure that the result of applying a positional embedding algorithm does not coincidently represent another token? E.g how to avoid that the positional embedding of “dog” in oosition i does not mean “cat” in position b?
Indeed, it is possible for a word at position i to have the same embedding as a different word at position j, since both positional information and non-positional semantic information are represented in the same embedding space. The model learns to use them appropriately during training.
Great video! What value is used for Theta?
Theta_i = 10000^(2i / d). I didn't cover this in the video, but it is mentioned in the RoFormer paper.
@@EfficientNLP That seems to be the same as the one used in the paper "Attention is All you Need".
Why is kv cache difficult to implement in case of relative embeddings?
The KV cache saves the K and V matrices during autoregressive decoding to avoid recomputing them for every token. But for relative embeddings, when a new token is generated, the relative distance between the new token and previous tokens changes. So there is an extra step (adding the relative biases) that cannot be cached, making the KV cache not as effective.
@@EfficientNLP Ah so to be precise, the cache can work but we need to fully compute the attention matrix and add the relative embedding matrix to it.
But isn't the attention matrix computed when we torch.matmul q and k in other cases too?
That is correct. In summary: there are several steps that are required in relative positional embeddings that aren't needed for absolute & rotary embeddings, which make them slower. Determining precisely which step causes the slowdown is an interesting question and would require some benchmarking experiments.
What is W (q,k) matrix and how its calculated?
These are the W_q and W_k matrices in self-attention, which are used to generate the Q and K matrices.
Why not positionally embed based on sentence and paragraph rather than just the position of the word in the overall prompt?
I understand that it adds more computation. But would yield better results wouldn't it?
The transformer doesn't distinguish between sentences and paragraphs; they are treated like any other token, so the position encoding doesn't refer to them specifically.
@@EfficientNLP I guess I have something in mind that I'm unable to express in words now. Will try it out and let you know what I ran into.