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Efficient Pareto Manifold Learning with Low-Rank Structure
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Proposes LORPMAN, which learns a Pareto manifold of networks as a shared main network plus per-task low-rank matrices with orthogonal regularization, cutting parameters versus PaMaL while improving hypervolume especially with many tasks.
Problem
Continuous Pareto front approximation for multi-task learning via linear combinations of base networks (PaMaL) scales poorly in parameters and convergence when the number of tasks is large.
Approach
Replace the m independent base networks of PaMaL with one main network plus m low-rank matrices per layer, combined by the preference vector, and add an orthogonality regularizer among the low-rank matrices so the main network captures shared features while the low-rank terms capture task-specific differences.
Key results
- On CIFAR-100 with 20 tasks, LORPMAN reaches HV 0.887 (x10^-2) versus 0.0583 for PaMaL, using 8.9% of PaMaL's parameters.
- On MultiMNIST, LORPMAN achieves HV 0.918 versus 0.905 for PaMaL and 0.906 for PHN-HVI.
- On CelebA with 40 tasks, LORPMAN achieves HV 1.167 (x10^-2) versus 0.472 for PaMaL using about 21% of its parameters.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| replace PaMaL's task-specific base networks with a shared main network and low-rank matrices | LORPMAN · MultiMNIST | HV: 0.905 (0.0010) -> 0.918 (0.0018) | Helped |
| replace PaMaL's task-specific base networks with a shared main network and low-rank matrices | LORPMAN · CIFAR-100 | HV (× 10^-2): 0.0583 (0.010) -> 0.887 (0.047) | Helped |
| replace PaMaL's task-specific base networks with a shared main network and low-rank matrices | LORPMAN · CelebA | HV (× 10^-2): 0.472 (0.018) -> 1.167 (0.008) | Helped |
| add orthogonal regularization (ablation) | LORPMAN · UTKFace | HV: 0.309 (0.002) -> 0.314 (0.001) | Helped |
| increase rank from 4 to 64 (ablation) | LORPMAN · UTKFace | HV: 0.306 (0.002) -> 0.314 (0.001) | Helped |
| increase rank from 64 to 128 (ablation) | LORPMAN · UTKFace | HV: 0.314 (0.001) -> 0.313 (0.002) | Hurt |
| freeze the main module at epoch 80 instead of leaving it unfrozen (epoch 100) (ablation) | LORPMAN · UTKFace | HV: 0.307 (0.003) -> 0.314 (0.001) | Helped |
| set scaling factor s within 0.1–1 rather than s=2 (ablation) | LORPMAN · UTKFace | HV: 0.310 (0.002) to 0.314 (0.001) | No clear effect |
Surprising findings
- PaMaL performs very poorly on CIFAR-100 (HV 0.0583 x10^-2) and simply increasing its learning rate does not fix convergence.
- Orthogonal regularization reduces average correlation among low-rank matrices from 0.466 to 0.067 on UTKFace.
Limitations
- Uses the same rank for all layers, which the authors note as a limitation.
- Orthogonal regularization uses stochastic approximation with subsets of 3 tasks when m exceeds 3, which is an approximation.
- Approximation theorem is a universal-approximation style existence result and does not guarantee training finds it.
Experimental setup
Datasets: MultiMNIST Census UTKFace CIFAR-100 CelebA CityScapes
Benchmarks: MultiMNIST Census UTKFace CIFAR-100 CelebA CityScapes
Metrics: hypervolume number of parameters mIoU pixel accuracy absolute error relative error
Baselines: PHN PHN-HVI COSMOS PaMaL EPO PMTL MOO-SVGD PNG GMOOAR LS UW MGDA
Builds on: PaMaL COSMOS Pareto hypernetworks LoRA multi-forward regularization
Closest papers by meaning
- Pareto Low-Rank Adapters: Efficient Multi-Task Learning with Preferences (ICLR 2025 · similarity 0.86)
- IOP: An Idempotent-Like Optimization Method on the Pareto Front of Hypernetwork (AAAI 2025 · similarity 0.86)
- StelLA: Subspace Learning in Low-rank Adaptation using Stiefel Manifold (NeurIPS 2025 · similarity 0.84)
- Task Groupings Regularization: Data-Free Meta-Learning with Heterogeneous Pre-trained Models (ICML 2024 · similarity 0.84)
- Towards Principled Task Grouping for Multi-Task Learning (NeurIPS 2026 · similarity 0.83)
- DMTG: One-Shot Differentiable Multi-Task Grouping (ICML 2024 · similarity 0.83)
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