Research map / Probabilistic and scientific modeling / Bayesian optimization
Joint Composite Latent Space Bayesian Optimization
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Proposes JoCo, which jointly trains neural encoders for high-dimensional inputs and intermediate outputs together with GP surrogates in a composite BO loop, outperforming high-dimensional BO baselines on nine composite tasks including LLM and text-to-image adversarial prompt attacks.
Problem
Bayesian optimization of composite functions f = g∘h where both the input x and the intermediate output h(x) are high-dimensional, making standard GP surrogates and prior composite BO methods ineffective or intractable.
Approach
Jointly train input and outcome neural encoders with multi-output GP surrogates (for h in latent space) and a GP on the latent outcome (for f), using the composite objective as supervision, and update all components continuously during BO with Thompson sampling inside a TuRBO trust region.
Key results
- JoCo outperforms baselines (Vanilla BO w/ DKL, TuRBO, CMA-ES, random) across all nine high-dimensional composite BO tasks, with especially strong early-optimization gains on toxic text and image generation.
- On held-out RMSE, the JoCo architecture beats GP+DKL and plain GP on all nine tasks (e.g., Dog Image Gen 1.844 vs 5.741; Env Model 4.191 vs 6.351).
- Removing joint training, continuous model updating, or trust regions significantly degrades JoCo performance, especially on generative AI tasks.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use JoCo's jointly trained latent encoders and probabilistic models instead of a standard approximate GP | JoCo architecture · All nine held-out task datasets | RMSE | Helped |
| Add a deep kernel to the approximate GP | Approximate GP · All nine held-out task datasets | RMSE | Helped |
| Remove continuous model updates during optimization (ablation) | JoCo · Optimization tasks, especially generative AI tasks | optimization performance | Hurt |
| Replace joint updates with separate updates of the input/outcome model and reward model (ablation) | JoCo · Optimization tasks | optimization performance | Hurt |
| Remove the TuRBO trust region (ablation) | JoCo · All tasks | optimization performance | Hurt |
| Do not propagate uncertainty through estimated outcomes (ablation) | JoCo · Optimization tasks | optimization performance | Hurt |
| Do not propagate uncertainty through estimated rewards (ablation) | JoCo · Optimization tasks | optimization performance | Hurt |
| Use expected improvement instead of Thompson sampling (ablation) | JoCo · Optimization tasks | optimization performance | Hurt |
| Vary the outcome encoder's latent dimension (ablation) | JoCo · Toxic Text Gen | optimization performance | No clear effect |
| Vary the number of update epochs, using a nonzero number of epochs (ablation) | JoCo · Optimization tasks | optimization performance | No clear effect |
| Vary the number of recent data points used for updates (ablation) | JoCo · Optimization tasks | optimization performance | No clear effect |
| Vary the learning rate (ablation) | JoCo · Optimization tasks | optimization performance | No clear effect |
Surprising findings
- On some synthetic and PDE tasks, baselines such as TuRBO eventually catch up to JoCo after many evaluations, with JoCo's advantage concentrated early in optimization.
Limitations
- Compositional BO baseline (Maus et al./EI-CF) is intractable for high-dimensional outputs, so not compared directly on most tasks.
- Some baselines catch up to JoCo after sufficiently many evaluations on several tasks.
- Requires choosing encoder architectures and hyperparameters per task (e.g., latent dimension 32), with limited theoretical analysis.
Experimental setup
Datasets: synthetic composite Langermann and Rosenbrock functions environmental modeling problem Brusselator PDE task rover trajectory planning task toxic text classifier and Emotion English sentiment classifier ImageNet ResNet18 classifier objective
Benchmarks: Langermann Rosenbrock Env Model PDE Rover Toxic Text Gen Aircraft Image Gen Dog Image Gen Sportscar Image Gen
Metrics: best objective value vs function evaluations RMSE of held-out predictions runtime and memory
Baselines: Vanilla BO with DKL TuRBO CMA-ES random sampling EI-CF TS-CF SAASBO
Builds on: TuRBO deep kernel learning compositional Bayesian optimization parametric GP regression
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