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MultiMax: Sparse and Multi-Modal Attention Learning
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Proposes MultiMax, a piecewise-differentiable, learnable replacement for SoftMax that modulates small and large input entries with separate temperatures to get both sparsity and multi-modality, improving ImageNet, WikiText-103 and IWSLT results.
Problem
SoftMax spreads probability mass onto irrelevant entries (poor sparsity), while existing sparse SoftMax variants need alternative losses, lose multi-modality, and have unstable training; a sparsity-multi-modality trade-off limits SoftMax expressivity.
Approach
Apply learnable piecewise (first- and second-order) modulation to the SoftMax input, using a low temperature for small entries (sparsity) and a high temperature for large entries (multi-modality), keeping full support and standard cross-entropy training.
Key results
- On ImageNet1K, DeiT-small with MultiMax in attention and output reaches 81.0% vs 80.4% SoftMax; DeiT-base reaches 82.6% vs 82.1%.
- On WikiText-103 with a 6-layer decoder, MultiMax in attention and output lowers test perplexity from 29.4 to 28.7.
- On IWSLT14 De-En, MultiMax scores 34.7 BLEU, on par with EvSoftMax (34.7) and above SoftMax (34.4); it adds ~40% training time in native PyTorch, ~10% with jit fusion.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Replace SoftMax with MultiMax in attention and output layers | DeiT-tiny · ImageNet-1k | accuracy (%): 72.8 -> 73.4 | Helped |
| Replace SoftMax with MultiMax in attention and output layers | DeiT-small · ImageNet-1k | accuracy (%): 80.4 -> 81.0 | Helped |
| Use Ev-SoftMax in attention instead of SoftMax | DeiT-small · ImageNet-1k | accuracy (%): 80.4 -> 80.0 | Hurt |
| Replace SoftMax with MultiMax in attention and output layers | DeiT-base · ImageNet-1k | accuracy (%): 82.1 -> 82.6 | Helped |
| Apply MultiMax in attention and output layers rather than Patch Diversification | DeiT-small · ImageNet-1k | accuracy (%): 81.2* vs 81.2 | No clear effect |
| Apply MultiMax in attention and output layers rather than AttnScale | DeiT-small · ImageNet-1k | accuracy (%): 80.9* -> 81.3 | Helped |
| Add MultiMax in attention only | 6-layer Transformer Decoder, 156M parameters · WikiText-103 test | perplexity: 29.4 -> 29.0 | Helped |
| Add MultiMax to the output layer in addition to attention | 6-layer Transformer Decoder, 156M parameters · WikiText-103 test | perplexity: 29.0 -> 28.7 | Helped |
| Replace SoftMax with MultiMax in attention | Transformer · IWSLT 2014 English-to-German | BLEU: 34.4 ± 0.07 -> 34.7 ± 0.07 | Helped |
| Add term (1), modulating smaller entries (ablation) | MultiMax on DeiT-small · ImageNet-1k | accuracy (%): 80.4 -> 80.6 | Helped |
| Add term (2), modulating larger entries, in addition to term (1) (ablation) | MultiMax on DeiT-small · ImageNet-1k | accuracy (%): 80.6 -> 80.7 | Helped |
| Add second-order terms to terms (1) and (2) (ablation) | MultiMax on DeiT-small · ImageNet-1k | accuracy (%): 80.7 -> 81.0 | Helped |
Surprising findings
- Ev-SoftMax training did not converge (accuracy below 10%) when used in the output layer on ImageNet.
- Learned MultiMax parameters show the first two attention layers are less sparse than SoftMax, contrary to deeper layers.
Limitations
- Native PyTorch implementation adds notable training overhead unless fused; no custom CUDA kernel.
- Several comparisons on ImageNet are single-run, and some baselines are not strictly comparable in training setup.
- Sparse SoftMax baselines were excluded from ImageNet classification due to training instability, limiting comparison.
Experimental setup
Datasets: ImageNet1K WikiText-103 IWSLT-2014 German-English
Benchmarks: ImageNet1K WikiText-103 IWSLT-2014 En-De
Metrics: top-1 accuracy perplexity BLEU patch similarity sparsity multi-modality
Baselines: SoftMax Top-k attention Ev-SoftMax SparseMax EntMax-1.5 Patch Diversification AttnScale
Builds on: SoftMax Sparsemax EntMax Ev-SoftMax DeiT
Closest papers by meaning
- Bridging the Divide: Reconsidering Softmax and Linear Attention (NeurIPS 2024 · similarity 0.88)
- Sparse Attention as Compact Kernel Regression (NeurIPS 2026 · similarity 0.87)
- Low-Rank Approximation for Sparse Attention in Multi-Modal LLMs (CVPR 2024 · similarity 0.87)
- Degrees of Freedom for Linear Attention: Distilling Softmax Attention with Optimal Feature Efficiency (NeurIPS 2025 · similarity 0.87)
- AdaSplash: Adaptive Sparse Flash Attention (ICML 2025 · similarity 0.87)
- Transformers Learn Faster with Semantic Focus (NeurIPS 2025 · similarity 0.86)
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