Terms in LLM architecture Part 1 - Embeddings Input and Output & positional encoding

Input Embedding - 

Input embedding is a technique used in natural language processing (NLP) and machine learning to represent words, phrases, or sentences as vectors of real numbers in a continuous vector space. It is a fundamental step in many NLP tasks, such as text classification, sentiment analysis, and machine translation.

Word Embeddings:

At the core of input embedding is the idea of word embeddings. Words are initially represented as discrete symbols (e.g., "dog," "cat," "house"), but these symbols lack the semantic relationships between words. Word embeddings aim to capture the meaning of words by representing them as dense vectors in a continuous vector space.

Continuous Vector Space:

In a continuous vector space, semantically similar words are closer to each other, and relationships between words (e.g., king - man + woman = queen) can be expressed as vector operations. This allows machine learning models to learn relationships and similarities between words based on the context in which they appear.

Training Word Embeddings:

Word embeddings are often trained using unsupervised learning on large text corpora. Popular algorithms for training word embeddings include Word2Vec, GloVe (Global Vectors for Word Representation), and FastText.

Input Embedding Layer:

In NLP models, an input embedding layer is added at the beginning of the network architecture. This layer transforms the input sequences (words or tokens) into their corresponding word embeddings. Each word in the input sequence is replaced by its embedding vector.

Learnable Parameters:

The embedding layer has learnable parameters that are adjusted during the training process. These parameters determine the mapping from discrete word indices to continuous vector representations.

Contextual Embeddings:

For more advanced NLP tasks, contextual embeddings are used. Contextual embeddings consider the context of each word in a sentence, capturing variations in meaning based on surrounding words. Models like BERT and GPT have been successful in capturing contextual embeddings 

In general embeddings provide a richer representation of input data enabling model to better understand the semantic relationship within the text. It enables the model to capture the semantic relationships, generalise to unseen words, and improve performance on downstream NLP tasks. 

Output Embedding 

Output embeddings, similar to input embeddings, are representations of data in a continuous vector space. In the context of natural language processing (NLP) or machine learning, output embeddings are often associated with the representations of the model's output, which can include words, phrases, or entire sentences.

Word Output Embeddings:

In tasks like language modeling or text generation, where the model is trained to predict the next word in a sequence, output embeddings represent the predicted words. These embeddings are used to generate the probability distribution over the vocabulary, and the word with the highest probability is chosen as the predicted next word.

Sequence Output Embeddings:

In sequence-to-sequence tasks, such as machine translation or text summarization, the model produces an output sequence. The output embeddings represent each element (word or token) in the generated sequence.

Sentence Output Embeddings:

In tasks like sentiment analysis or document classification, the model predicts a label or sentiment for an entire sentence or document. The output embeddings represent the features used for making the final prediction.

Contextual Embeddings:

Similar to contextual embeddings in input embeddings, models may generate contextual embeddings for the output sequence. These embeddings take into account the context of the entire sequence, capturing dependencies and relationships between different elements.

Learnable Parameters:

Output embeddings, like input embeddings, have learnable parameters. These parameters are adjusted during the training process to improve the model's ability to generate meaningful and coherent output sequences.

Applications:

Output embeddings play a crucial role in various NLP applications, including machine translation, text summarization, image captioning, and conversational AI. They are used to represent the model's generated output in a way that preserves semantic relationships and captures the nuances of the task.

Embedding Layers:

In neural network architectures, embedding layers are often used for both input and output embeddings. These layers map discrete indices (such as word indices) to continuous vector representations.

Positional Encoding :

Positional encoding is a technique used in natural language processing (NLP) and machine learning, specifically in the context of sequence-to-sequence models and attention mechanisms. It is employed to provide information about the positions of elements in a sequence, such as the order of words in a sentence, which is not inherently captured by standard embedding techniques.

In models like the Transformer architecture, which is widely used in NLP tasks, positional encoding is added to the input embeddings to give the model information about the positions of tokens in a sequence. The reason for using positional encoding is that traditional embedding methods, such as Word2Vec or GloVe, do not inherently encode information about the order or position of words in a sentence.