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How Sparse Attention Approximates Exact Attention? Your Attention is Naturally $n^C$-Sparse

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arxiv 2404.02690 v2 pith:F2G5NSHZ submitted 2024-04-03 cs.LG cs.AIcs.CL

classification cs.LGcs.AIcs.CL
keywords attentionsparseentriesapproximatesbulletcomputationalphaefficient
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abstract

Sparse Attention is a technique that approximates standard attention computation with sub-quadratic complexity. This is achieved by selectively ignoring smaller entries in the attention matrix during the softmax function computation. Variations of this technique, such as pruning KV cache, sparsity-based fast attention, and Sparse Transformer, have been extensively utilized for efficient Large Language Models (LLMs) deployment. Despite its widespread use, a theoretical understanding of the conditions under which sparse attention performs on par with traditional attention remains elusive. This work aims to $\textbf{bridge this gap by examining the inherent sparsity of standard attention processes}$. Our theoretical framework reveals several brand-new key insights: $\bullet$ Attention is $n^{C}$-sparse, implying that considering only the largest $\Omega(n^{C})$ entries out of all $n$ entries is sufficient for sparse attention to approximate the exact attention matrix with decreasing loss. Here, $n$ represents the input length and $C \in (0, 1)$ is a constant. $\bullet$ Stable $o(\log(n))$-sparse attention, which approximates attention computation with $\log(n)$ or fewer entries, may not be feasible since the error will persist at a minimum of $O(1)$. $\bullet$ An adaptive strategy ($\alpha \cdot n^C, \alpha \in \mathbb{R}$) for the window size of efficient attention methods rather than a fixed one is guaranteed to perform more accurately and efficiently in a task for inference on flexible context lengths.

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Cited by 5 Pith papers

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    cs.IR 2025-07 conditional novelty 6.0 of 10

    EARN inserts learnable register tokens at both ends of a user prompt, prunes prompt tokens after early layers, and achieves up to 3.79x faster LLM-based recommendation inference with comparable or better accuracy.

  2. SALE : Low-bit Estimation for Efficient Sparse Attention in Long-context LLM Prefilling

    cs.LG 2025-05 conditional novelty 6.0 of 10

    SALE is a training-free sparse attention method that uses 4-bit quantized query-key estimates and a relative attention score to skip unimportant blocks, achieving over 3.36x prefill speedup on 64K+ token contexts with...

  3. SPADE: An Input-Adaptive Sparse Attention Engine for Fast Video Diffusion Models Inference

    cs.CV 2026-08 conditional novelty 5.0 of 10

    SPADE combines static, semi-static, and dynamic block-sparse attention with a cheap SICS-based blocking heuristic to speed up video diffusion inference by up to 1.80x end-to-end.

  4. DeltaLLM: A Training-Free Framework Exploiting Temporal Sparsity for Efficient Edge LLM Inference

    cs.AI 2025-07 conditional novelty 5.0 of 10

    DeltaLLM exploits temporal sparsity in key vectors (delta encoding) with a hybrid local-window attention to cut attention computation by up to 60% on 1-2B parameter LLMs with minimal accuracy loss.

  5. Unifying Learning Dynamics and Generalization in Transformers Scaling Law

    cs.LG 2025-12 reject novelty 4.0 of 10

    Claims a two-stage transformer scaling law (exponential then C^{-1/6}) with matching bounds, but the lower bounds are missing, the exponent is inconsistent (-1/7 vs -1/6), and the law is an artifact of hand-set M = Θ(...

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