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ModHiFi: Identifying High Fidelity predictive components for Model Modification
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Proposes ModHiFi, a data-free, loss-free model modification method that scores components by singleton Subset Fidelity (from synthetic data) to perform structured pruning and classwise unlearning on CNNs, ViTs/Swin, and LLMs.
Problem
Modifying well-trained open-weight models (structured pruning and classwise unlearning) without training data, the loss function, or gradients, using only distributional access such as synthetic data.
Approach
Defines Subset Fidelity, the fraction of a layer's output a subset of input contributions can reconstruct after optimal weight compensation; proves global error is linearly bounded by local reconstruction error for Lipschitz networks, and that top-k singleton fidelity is optimal when input contributions are uncorrelated.
Key results
- ModHiFi-P on ResNet50/ImageNet reaches 73.82% accuracy at 3.66x FLOP reduction and 2.42x CPU speedup, versus 73.80% for DFPC at 3.46x FLOP and 2.37x CPU speedup.
- On Llama-2-7B at 10% sparsity, ModHiFi-P-Alpaca reaches WikiText PPL 6.36 and 65.96 average zero-shot accuracy versus 6.46 PPL and 59.96 for SliceGPT.
- ModHiFi-U achieves 0.2% forget accuracy on CIFAR-10 ResNet-50 without fine-tuning in 10 seconds, with 92.98% remain accuracy, versus 3.54% forget accuracy and 363 seconds for Jia et al.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use ModHiFi-P instead of DFPC at the reported CIFAR-10 pruning setting | ResNet-50 structured pruning · CIFAR-10 | accuracy: 90.25 -> 91.02 | Helped |
| Use ModHiFi-P instead of L2 w/ ST at the reported CIFAR-10 pruning setting | ResNet-50 structured pruning · CIFAR-10 | accuracy: 90.12 -> 91.02 | Helped |
| Use ModHiFi-P instead of DFPC (30) | ResNet-50 structured pruning · ImageNet | accuracy: 75.9 -> 76.70 | Helped |
| Use ModHiFi-P instead of DFPC (54) | ResNet-50 structured pruning · ImageNet | CPU Speedup: 2.37x -> 2.42x | Helped |
| Use Alpaca rather than WikiText-2 for calibration (ablation) | ModHiFi-P on Llama-2-7B at 10% sparsity · Llama-2-7B, 10% sparsity | Average task accuracy: 64.23 -> 65.96 | Helped |
| Use Alpaca rather than WikiText-2 for calibration (ablation) | ModHiFi-P on Llama-2-7B at 20% sparsity · Llama-2-7B, 20% sparsity | Average task accuracy: 57.16 -> 60.62 | Helped |
| Use Alpaca rather than WikiText-2 for calibration (ablation) | ModHiFi-P on Llama-2-7B at 30% sparsity · Llama-2-7B, 30% sparsity | Average task accuracy: 48.63 -> 52.44 | Helped |
| Add Gaussian noise (standard deviation 0.01) to 20% of HiFi components rather than perturbing 80% of non-HiFi components (ablation) | ResNet-50 · CIFAR-10 | accuracy drop: around 12% vs 1% | Hurt |
| Add Gaussian noise (standard deviation 0.02) to 50% of HiFi components rather than 50% of non-HiFi components (ablation) | ResNet-50 · CIFAR-10 | accuracy drop: 85% vs around 1.4% | Hurt |
| Use higher-quality synthetic calibration samples (ablation) | ModHiFi-P · Structured pruning experiments | sparsity-accuracy tradeoff | Helped |
| Fine-tune ModHiFi-U for three epochs on synthetic samples (ablation) | Swin-Transformer classwise unlearning · CIFAR-10 | unlearning performance | Helped |
| Fine-tune ModHiFi-U for 10 epochs using synthetic samples rather than no fine-tuning (ablation) | Swin-Transformer classwise unlearning · CIFAR-10 | forget accuracy | Helped |
Surprising findings
- Well-trained transformers are empirically found to be Lipschitz continuous on bounded domains, contrary to prior assertions in the literature.
- On Swin-T, ModHiFi-U without fine-tuning falls well short of the state of the art (8.83% forget accuracy, 73.57% remain accuracy).
Limitations
- Theoretical bounds rely on local Lipschitz continuity, which is not guaranteed at initialization and only empirically verified for trained models.
- Optimality of singleton selection holds only under uncorrelated input contributions, an assumption that rarely holds exactly in practice.
- Attention-specific analysis is left for future work; the analysis focuses on the FFN; Swin-T unlearning without fine-tuning underperforms baselines.
Experimental setup
Datasets: CIFAR-10 CIFAR-100 ImageNet WikiText-2 Alpaca
Benchmarks: ImageNet CIFAR-10 CIFAR-100 WikiText-2 perplexity ARC-e ARC-c PIQA WinoGrande HellaSwag
Metrics: top-1 accuracy FLOP reduction parameter reduction CPU speedup GPU speedup perplexity zero-shot accuracy forget accuracy retain accuracy unlearning time
Baselines: GReg-2 OTO DepGRAPH ThiNet DFPC L2 norm pruning SliceGPT ShortGPT Gradient Ascent Jia et al. unlearning
Builds on: Optimal Brain Surgeon-style reconstruction pruning ShortGPT SliceGPT DFPC
Closest papers by meaning
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