Fractal Analysis of GPT-2 Token Embedding Spaces: Stability and Evolution of Correlation Dimension

초록

This paper explores the fractal properties of token embedding spaces in GPT-2 language models by analyzing the stability of the correlation dimension, a measure of geometric complexity. Token embeddings represent words or subwords as vectors in a high-dimensional space. We hypothesize that the correlation dimension D2 remains consistent across different vocabulary subsets, revealing fundamental structural characteristics of language representation in GPT-2. Our main objective is to quantify and analyze the stability of D2 in these embedding subspaces, addressing the challenges posed by their high dimensionality. We introduce a new theorem formalizing this stability, stating that for any two sufficiently large random subsets S1,S2 subset of E, the difference in their correlation dimensions is less than a small constant epsilon. We validate this theorem using the Grassberger-Procaccia algorithm for estimating D2, coupled with bootstrap sampling for statistical consistency. Our experiments on GPT-2 models of varying sizes demonstrate remarkable stability in D2 across different subsets, with consistent mean values and small standard errors. We further investigate how the model size, embedding dimension, and network depth impact D2. Our findings reveal distinct patterns of D2 progression through the network layers, contributing to a deeper understanding of the geometric properties of language model representations and informing new approaches in natural language processing.

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