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Pretraining Codomain Attention Neural Operators for Solving Multiphysics PDEs
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Proposes CoDA-NO, a transformer neural operator that tokenizes PDE solutions along the codomain (physical variables) with function-space attention, normalization and positional encoding, pretrained with masked reconstruction for few-shot adaptation to multiphysics PDEs.
Problem
Neural operators struggle to solve coupled multiphysics PDEs with complex geometries, interacting variables, and scarce high-resolution data, and existing PDE foundation models cannot handle varying numbers of physical variables or irregular meshes.
Approach
Treat each physical variable (codomain component) as a token function and extend self-attention, positional encoding, and normalization to function spaces (with FNO/GNO operators for Q/K/V), so a single model can be pretrained by masked reconstruction on one PDE system and fine-tuned to systems with new variables.
Key results
- Pretrained CoDA-NO achieves 0.024 L2 error on NS at Re=400 with 5 few-shot samples, versus 0.200 for GINO and 0.038 for GNN (best baseline).
- On Rayleigh-Benard with Ra=12e3 and 5 shots, pretrained CoDA-NO reaches 0.016 versus 0.049 for U-Net, roughly a factor-of-two or more reduction.
- On PDEBench, CoDA-NO reduces test error by up to 43% over FNO while using only about 2% of its parameters.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Pretrain CoDA-NO on NS+EW rather than train from scratch | CoDA-NO · Fluid-structure interaction, NS+EW, Re = 400, 5 shots | L2 loss: 0.051 -> 0.040 | Helped |
| Pretrain CoDA-NO on NS+EW rather than train from scratch | CoDA-NO · Fluid-structure interaction, NS+EW, Re = 4000, 5 shots | L2 loss: 0.326 -> 0.308 | Helped |
| Pretrain CoDA-NO on NS before fine-tuning on the new temperature variable | CoDA-NO · Rayleigh-Bénard convection, Ra =12×10^3, 5 shots | L2 error: 0.067 -> 0.016 | Helped |
| Add codomain attention (ablation) | CoDA-NO · Fluid-structure interaction, NS+EW, 5 shots | L2 loss: 0.211 -> 0.040 | Helped |
| Add function-space normalization (ablation) | CoDA-NO pretrained on NS+EW · Fluid-structure interaction, NS+EW, 5 shots | L2 loss: 0.232 -> 0.040 | Helped |
| Add VSPE (ablation) | CoDA-NO pretrained on NS+EW · Fluid-structure interaction, NS+EW, 5 shots | L2 loss: 0.057 -> 0.040 | Helped |
| Add pretraining (ablation) | CoDA-NO with VSPE and normalization · Fluid-structure interaction, NS+EW, 5 shots | L2 loss: 0.211 -> 0.040 | Helped |
| Add function-space normalization (ablation) | CoDA-NO pretrained on NS · Fluid-structure interaction, NS+EW, 5 shots | L2 loss: 0.079 -> 0.071 | Helped |
| Replace codomain attention with regular patch-based attention (ablation) | CoDA-NO · Fluid-structure interaction | L2 loss | Hurt |
| Freeze the Encoder and train only the Predictor and VSPEs (ablation) | CoDA-NO fine-tuning · Fluid-structure interaction | L2 loss | Helped |
Surprising findings
- Removing the normalization layer prevented CoDA-NO from converging.
- Larger baseline models (e.g., GINO at 200M parameters) overfit and perform worse in few-shot settings.
Limitations
- Performance on target PDEs depends on the number of training examples.
- No physics-informed constraints are integrated.
- Higher computational cost and parameter count than several baselines.
Experimental setup
Datasets: NS dataset (TurtleFSI generated) NS+EW fluid-structure interaction dataset (TurtleFSI generated) Rayleigh-Benard convection dataset (generated) PDEBench subset
Benchmarks: fluid-structure interaction NS and NS+EW datasets Rayleigh-Benard convection PDEBench
Metrics: L2 relative error zero-shot super-resolution error parameter count inference and training time
Baselines: GINO DeepONet GNN ViT U-Net FNO
Builds on: Fourier neural operator graph neural operator GINO transformer self-attention instance normalization
Closest papers by meaning
- Data-Efficient Operator Learning via Unsupervised Pretraining and In-Context Learning (NeurIPS 2024 · similarity 0.88)
- Improved Operator Learning by Orthogonal Attention (ICML 2024 · similarity 0.87)
- Positional Knowledge is All You Need: Position-induced Transformer (PiT) for Operator Learning (ICML 2024 · similarity 0.87)
- Neural Interpretable PDEs: Harmonizing Fourier Insights with Attention for Scalable and Interpretable Physics Discovery (ICML 2025 · similarity 0.86)
- RIGNO: A Graph-based Framework For Robust And Accurate Operator Learning For PDEs On Arbitrary Domains (NeurIPS 2025 · similarity 0.86)
- DPOT: Auto-Regressive Denoising Operator Transformer for Large-Scale PDE Pre-Training (ICML 2024 · similarity 0.86)
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