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RNNs are not Transformers (Yet): The Key Bottleneck on In-context Retrieval

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arxiv 2402.18510 v4 pith:7VCS4PN7 submitted 2024-02-28 cs.LG cs.CLstat.ML

RNNs are not Transformers (Yet): The Key Bottleneck on In-context Retrieval

classification cs.LG cs.CLstat.ML
keywords rnnstransformersbottleneckcapabilitycontextin-contextproblemsprove
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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This paper investigates the gap in representation powers of Recurrent Neural Networks (RNNs) and Transformers in the context of solving algorithmic problems. We focus on understanding whether RNNs, known for their memory efficiency in handling long sequences, can match the performance of Transformers, particularly when enhanced with Chain-of-Thought (CoT) prompting. Our theoretical analysis reveals that CoT improves RNNs but is insufficient to close the gap with Transformers. A key bottleneck lies in the inability of RNNs to perfectly retrieve information from the context, even with CoT: for several tasks that explicitly or implicitly require this capability, such as associative recall and determining if a graph is a tree, we prove that RNNs are not expressive enough to solve the tasks while Transformers can solve them with ease. Conversely, we prove that adopting techniques to enhance the in-context retrieval capability of RNNs, including Retrieval-Augmented Generation (RAG) and adding a single Transformer layer, can elevate RNNs to be capable of solving all polynomial-time solvable problems with CoT, hence closing the representation gap with Transformers.

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Forward citations

Cited by 7 Pith papers

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