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On Neural Networks as Infinite Tree-Structured Probabilistic Graphical Models
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Constructs an infinite-width tree-structured Markov network whose inference exactly reproduces sigmoid DNN forward passes and gradients, and uses this to motivate HMC-based contrastive-divergence fine-tuning for calibration.
Problem
Deep neural networks lack precise probabilistic semantics as probabilistic graphical models; it is unclear what joint distribution a DNN's forward pass approximates, and how PGM inference tools could be applied to DNNs.
Approach
Unroll any sigmoid DNN into an infinite-width treewidth-1 Markov network (copying parents and dividing weights by L); as L goes to infinity, marginal inference equals the sigmoid forward pass and the marginal likelihood gradient equals the cross-entropy gradient. This motivates HMC over continuous hidden variables with a normal approximation for contrastive-divergence fine-tuning.
Key results
- On synthetic BN/MN data, HMC with L=10 fine-tuning gave lower MAE than plain DNN in several settings (e.g., BN (0.3) at 100 epochs: 5.300e-3 vs 6.593e-3), with Gibbs often no better than DNN.
- On Covertype label 1 at 100 epochs, HMC-10 reduced test ECE from 4.207e-2 (DNN) to 2.352e-2.
- Gibbs fine-tuning sometimes performed worse than the DNN, e.g., Covertype label 2 at 100 epochs: 7.796e-2 vs 4.268e-2 for DNN.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Synthetic BN (0.3), 100 train epochs | MAE (× 10^-3): 6.593 -> 5.300 | Helped |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Synthetic BN (0.3), 1000 train epochs | MAE (× 10^-3): 34.44 -> 23.53 | Helped |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Synthetic BN (3), 100 train epochs | MAE (× 10^-3): 72.76 -> 76.54 | Hurt |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Synthetic MN (0.3), 100 train epochs | MAE (× 10^-3): 6.031 -> 4.515 | Helped |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Synthetic MN (1), 100 train epochs | MAE (× 10^-3): 9.671 -> 8.887 | Helped |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Covertype label 1, 100 train epochs | ECE (× 10^-2): 4.207 -> 2.352 | Helped |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Covertype label 2, 100 train epochs | ECE (× 10^-2): 4.268 -> 7.719 | Hurt |
| Fine-tune with HMC using L=10 rather than leave the DNN unfine-tuned | DNN · Covertype label 2, 1000 train epochs | ECE (× 10^-2): 6.634 -> 5.233 | Helped |
| Use L=100 rather than L=10 for HMC fine-tuning (ablation) | HMC fine-tuning · Synthetic BN (0.3), 100 train epochs | MAE (× 10^-3): 5.300 -> 6.864 | Hurt |
| Use L=1000 rather than L=10 for HMC fine-tuning (ablation) | HMC fine-tuning · Synthetic BN (0.3), 100 train epochs | MAE (× 10^-3): 5.300 -> 6.658 | Hurt |
| Use L=100 rather than L=10 for HMC fine-tuning (ablation) | HMC fine-tuning · Synthetic MN (0.3), 100 train epochs | MAE (× 10^-3): 4.515 -> 6.382 | Hurt |
| Use L=1000 rather than L=10 for HMC fine-tuning (ablation) | HMC fine-tuning · Synthetic MN (0.3), 100 train epochs | MAE (× 10^-3): 4.515 -> 6.070 | Hurt |
Surprising findings
- Gibbs sampling in the constructed PGM, the theoretically consistent method, often calibrated worse than the plain DNN.
- Larger HMC L (1000) often reverted to DNN-level calibration, with small gains only for L=10.
Limitations
- The infinite tree construction is impractical; the result is an approximation to the direct PGM, and only sigmoid activations are proven exactly.
- Extension to ReLU, normalization layers and other activations is argued informally rather than proven.
- Empirical evaluation is limited to small synthetic datasets and one tabular dataset.
Experimental setup
Datasets: Synthetic BN/MN datasets (1000 points each) Covertype
Benchmarks: Synthetic BN/MN calibration Covertype (labels 1 and 2)
Metrics: mean absolute error expected calibration error t-test p-values
Baselines: SGD training Gibbs sampling HMC with L=100 HMC with L=1000
Builds on: contrastive divergence variable elimination conditional random fields Hamiltonian Monte Carlo
Closest papers by meaning
- PGM-Explainer: Probabilistic Graphical Model Explanations for Graph Neural Networks (NeurIPS 2020 · similarity 0.88)
- On the Expressive Power of Tree-Structured Probabilistic Circuits (NeurIPS 2024 · similarity 0.86)
- Explaining, Fast and Slow: Abstraction and Refinement of Provable Explanations (ICML 2025 · similarity 0.86)
- Sum-Product-Set Networks: Deep Tractable Models for Tree-Structured Graphs (ICLR 2024 · similarity 0.86)
- Probabilistic Neural Circuits (AAAI 2024 · similarity 0.85)
- [Re] GNNInterpreter: A probabilistic generative model-level explanation for Graph Neural Networks (NeurIPS 2024 · similarity 0.85)
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