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arXiv 2402.09963cs.LG
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为什么敏感函数对Transformer来说是困难的?

Why are Sensitive Functions Hard for Transformers?

Saarland Informatics Campus(萨尔兰信息学园区);Saarland University(萨尔兰大学)

Michael Hahn, Mark Rofin

AI总结:

本研究证明Transformer的损失景观受输入空间敏感性约束,敏感函数导致参数空间孤立点,从而产生低敏感性泛化偏差,统一解释了其学习困难,强调需结合损失景观理解归纳偏差。

摘要:

实证研究已经确定了Transformer的一系列可学习性偏差和局限性,例如在学习计算简单形式语言(如PARITY)时持续存在的困难,以及偏向于低度函数的倾向。然而,理论理解仍然有限,现有的表达能力理论要么过度预测,要么低估了现实的学习能力。我们证明,在Transformer架构下,损失景观受到输入空间敏感性的约束:输出对输入字符串的多个部分敏感的Transformer在参数空间中占据孤立点,导致泛化中出现低敏感性偏差。我们从理论上和实证上表明,这一理论统一了关于Transformer学习能力和偏差的广泛实证观察,例如它们对低敏感性和低度的泛化偏差,以及PARITY在长度泛化上的困难。这表明,理解Transformer的归纳偏差不仅需要研究其原则上的表达能力,还需要研究其损失景观。

英文摘要:

Empirical studies have identified a range of learnability biases and limitations of transformers, such as a persistent difficulty in learning to compute simple formal languages such as PARITY, and a bias towards low-degree functions. However, theoretical understanding remains limited, with existing expressiveness theory either overpredicting or underpredicting realistic learning abilities. We prove that, under the transformer architecture, the loss landscape is constrained by the input-space sensitivity: Transformers whose output is sensitive to many parts of the input string inhabit isolated points in parameter space, leading to a low-sensitivity bias in generalization. We show theoretically and empirically that this theory unifies a broad array of empirical observations about the learning abilities and biases of transformers, such as their generalization bias towards low sensitivity and low degree, and difficulty in length generalization for PARITY. This shows that understanding transformers' inductive biases requires studying not just their in-principle expressivity, but also their loss landscape.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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