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Rethinking Neural Nonlinearity as Gating
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Proposes Threshold Gating (TG), a primitive that rewrites standard activations (ReLU, SiLU, GELU, sigmoid, tanh, Hardtanh) and softmax as input-conditioned soft gates over K affine branches, enabling lossless conversion of pretrained nets and training gains.
Problem
Activation functions are conventionally treated as discrete, post-MAC nonlinearities; this is costly for analog in-memory hardware where ADC/DAC crossings dominate power and area. The paper asks whether nonlinearity can instead be expressed as a single universal gating primitive.
Approach
Reframe every standard activation as a sum of sigmoid-gated affine branches applied before the MAC (threshold gating with K=2 or 3 branches), show exact or near-exact closed-form conversions, extend to softmax via a sigmoid-of-LSE identity, and prove a minimal branch theorem linking K to trainability.
Key results
- Converting pretrained ViT-B/16 GELU to K=3 TG recovers 0.00% accuracy change (vs -1.09% generic K=2); exact activations like ReLU, SiLU, sigmoid, tanh convert at 0.00% accuracy drop.
- Converted SmolLM-135M and TinyLlama-1.1B keep WikiText-2 perplexity unchanged (0.00%), while GPT-2 drifts +0.22% due to GELU approximation.
- TG_W K=2 training-step speedup of 1.47-2.04x over baselines across four model-dataset pairs (3 seeds each); DeepSpeech2 WER improves 1.2-4.5 points with TG_A on LSTM gates.
Surprising findings
- Softmax admits an exact two-branch sigmoid conversion via softmax(z)_i = sigmoid(z_i - LSE(z_{-i})) with no fine-tuning, so converted LLMs keep their perplexity.
- Multiplicative (input-carrying) branches on LSTM gates degrade WER back to baseline, while constant-family gating wins at every hidden size.
Limitations
- TG kernels are not hand-optimized; wall-clock training may be slower, and speedup is reported in steps rather than time.
- Circuit-level implementation is only a reference topology; crossbar integration and silicon validation are future work.
- GELU conversion is approximate (K=2 residual ~0.3%) and needs per-layer calibration or K=3 to be exact.
Experimental setup
Datasets: ImageNet CIFAR-10 CIFAR-100 MNIST AN4 WikiText-2 OpenWebText MSD Hippocampus
Benchmarks: ImageNet CIFAR-10 CIFAR-100 MNIST AN4 WikiText-2 OpenWebText MSD Hippocampus
Metrics: top-1 accuracy perplexity word error rate Dice training-step speedup parameter count
Baselines: ReLU SiLU GELU LSTM with sigmoid/tanh gates Maxout SwiGLU
Builds on: SiLU GELU Mixture of Experts Highway Networks Hayou et al. edge-of-chaos analysis
Closest papers by meaning
- Analog Foundation Models (NeurIPS 2025 · similarity 0.86)
- Better NTK Conditioning: A Free Lunch from (ReLU) Nonlinear Activation in Wide Neural Networks (NeurIPS 2025 · similarity 0.85)
- DEEP NEURAL NETWORK INITIALIZATION WITH SPARSITY INDUCING ACTIVATIONS (ICLR 2024 · similarity 0.85)
- Towards Exact Gradient-based Training on Analog In-memory Computing (NeurIPS 2024 · similarity 0.85)
- Exploiting Symmetric Temporally Sparse BPTT for Efficient RNN Training (AAAI 2024 · similarity 0.84)
- Exact, Tractable Gauss-Newton Optimization in Deep Reversible Architectures Reveal Poor Generalization (NeurIPS 2024 · similarity 0.84)
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