When Can Transformers Count to n?
Keywords: Transformers, theory, counting, attention
TL;DR: We show theoretically and empirically that in order for transformers to solve simple counting tasks, their size must depend on either the dictionary size of the context length.
Abstract: Large language models based on the transformer architectures can solve highly complex tasks. But are there simple tasks that such models cannot solve? Here we focus on very simple counting tasks, that involve counting how many times a token in the vocabulary have appeared in a string. We show that if the dimension of the transformer state is linear in the context length, this task can be solved. However, the solution we propose does not scale beyond this limit, and we provide theoretical arguments for why it is likely impossible for a size limited transformer to implement this task. Our empirical results demonstrate the same phase-transition in performance, as anticipated by the theoretical argument. Our results demonstrate the importance of understanding how transformers can solve simple tasks.
Primary Area: learning theory
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Submission Number: 3977
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