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Scalable Kernel Inverse Optimization
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Extends inverse optimization to RKHS hypotheses with a kernelized suboptimality-loss SDP and proposes Sequential Selection Optimization (coordinate-descent-style block updates) to scale training on MuJoCo D4RL learning-from-demonstration tasks.
Problem
Inverse optimization learns the objective of an expert's forward optimization problem from data, but linear hypothesis classes are limited in expressiveness, and kernelized IO SDPs scale poorly (memory grows quadratically with dataset size).
Approach
Kernelize the quadratic FOP objective via a dual/LMI reformulation of the suboptimality loss so the problem becomes a finite-dimensional convex SDP over dual variables, and train it with a block coordinate method (SSO) that selects KKT-violating coordinates plus random ones, warm-started by solving sub-datasets.
Key results
- KIO with 5k-10k samples reaches normalized returns such as 109.9 on Hopper-expert and 50.2 on Hopper-medium, competitive with BC baselines in four of six tasks, while linear IO scores near zero on Walker2d and Halfcheetah.
- SSO converges to within about 1e-4 of the optimal objective (SCS) by 20 iterations on the six tasks, with errors below 0.1 by iteration 10.
- On 100k-sample medium-expert tasks, KIO reaches 79.6 (Hopper), 100.1 (Walker2d), and 46.4 (Halfcheetah) normalized return, where direct SDP solving ran out of memory.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| add the kernel method to IO | IO · Hopper-expert (D4RL) | normalized return: 31.8 -> 109.9 (5k) | Helped |
| add the kernel method to IO | IO · Hopper-medium (D4RL) | normalized return: 20.6 -> 50.2 (5k) | Helped |
| add the kernel method to IO | IO · Walker2d-expert (D4RL) | normalized return: 0.9 -> 108.5 (10k) | Helped |
| add the kernel method to IO | IO · Walker2d-medium (D4RL) | normalized return: 0.0 -> 74.6 (5k) | Helped |
| add the kernel method to IO | IO · Halfcheetah-expert (D4RL) | normalized return: -1.7 -> 84.4 (10k) | Helped |
| add the kernel method to IO | IO · Halfcheetah-medium (D4RL) | normalized return: -3.1 -> 39.0 (5k) | Helped |
| replace RBF kernel with Laplace kernel (ablation) | KIO · Hopper-medium, Hopper-expert, Walker2d-medium, Walker2d-expert, Halfcheetah-medium, Halfcheetah-expert (D4RL) | normalized return | Mixed |
| replace RBF kernel with linear kernel (ablation) | KIO · Hopper-medium, Hopper-expert, Walker2d-medium, Walker2d-expert, Halfcheetah-medium, Halfcheetah-expert (D4RL) | normalized return | Hurt |
| disable Heuristic Coordinates Selection (ablation) | SSO on Hopper-expert (D4RL) · Hopper-expert, first 5k points | objective function convergence | Hurt |
| disable the Warm-Up Trick (ablation) | SSO on Hopper-expert (D4RL) · Hopper-expert, first 5k points | objective function convergence | Hurt |
Surprising findings
- Linear-kernel KIO performs near zero on several tasks, showing the kernel is essential for learning from demonstrations.
- Plain IO without kernels fails on Walker2d and Halfcheetah (scores near 0 or negative).
Limitations
- Adding a new data point requires all training data to compute the FOP coefficients, so cost grows with dataset size.
- No theoretical convergence rate analysis for SSO.
- Memory use remains substantial (up to 256 GB at 100k data points) and initialization strongly affects SSO.
Experimental setup
Datasets: D4RL Hopper-expert D4RL Hopper-medium D4RL Walker2d-expert D4RL Walker2d-medium D4RL Halfcheetah-expert D4RL Halfcheetah-medium D4RL Hopper-medium-expert D4RL Walker2d-medium-expert D4RL Halfcheetah-medium-expert
Benchmarks: D4RL MuJoCo (Hopper, Walker2d, Halfcheetah)
Metrics: normalized return suboptimality objective gap
Baselines: IO (linear inverse optimization) BC(TD3+BC) BC(CQL) SCS
Builds on: inverse optimization suboptimality loss representer theorem sequential minimal optimization
Closest papers by meaning
- Inverse Optimization via Learning Feasible Regions (ICML 2025 · similarity 0.86)
- Automated Kernel Discovery Towards Understanding High-dimensional Bayesian Optimization (NeurIPS 2026 · similarity 0.85)
- Inverse M-Kernels for Linear Universal Approximators of Non-Negative Functions (NeurIPS 2024 · similarity 0.85)
- Adaptive Kernel Design for Bayesian Optimization Is a Piece of CAKE with LLMs (NeurIPS 2025 · similarity 0.85)
- Conformal Inverse Optimization (NeurIPS 2024 · similarity 0.85)
- Kernel-based guarantees for nonlinear parametric models in Bayesian optimization (NeurIPS 2026 · similarity 0.84)
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