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Tree-Guided Diffusion Planner
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Proposes TDP, a training-free zero-shot test-time planner that wraps a pretrained diffusion planner in a bi-level tree search (particle-guided parent trajectories plus gradient-guided fast-denoised child refinements) to handle non-convex, non-differentiable, and multi-reward guidance.
Problem
Test-time guided planning with pretrained diffusion planners fails when guide functions are non-convex, non-differentiable (e.g., intermediate-goal constraints), or multi-reward, because standard gradient guidance gets trapped in local optima and in-distribution trajectories.
Approach
Frames test-time planning as tree search with a bi-level sampling process: fixed-potential particle guidance on control states produces diverse parent trajectories, and fast partial re-denoising from random branch points with gradient guidance on observation states produces child trajectories; the best leaf is selected by the true guide score.
Key results
- On Maze2D gold-picking, TDP reaches 43.7 single-task and 72.4 multi-task average versus 21.1 and 44.9 for MCSS.
- On KUKA PnWP, TDP scores 66.81 versus 39.72 for AdaptDiffuser and 35.69 for MCSS.
- On AntMaze multi-goal, TDP finds 66.1 goals versus 61.3 for MCSS and reduces timesteps per goal to 558.4 from 612.1.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| add sub-tree expansion to parent trajectory sampling (ablation) | TDP · Maze2d Gold-picking, Single-task Average | performance: 24.7 -> 43.7 | Helped |
| add particle guidance to parent branching (ablation) | TDP · Maze2d Gold-picking, Single-task Average | performance: 40.1 -> 43.7 | No clear effect |
| add sub-tree expansion to parent trajectory sampling (ablation) | TDP · KUKA PnWP | performance: 35.53 -> 66.81 | Helped |
| add particle guidance to parent branching (ablation) | TDP · KUKA PnWP | performance: 66.63 -> 66.81 | No clear effect |
| add particle guidance to parent branching (ablation) | TDP · KUKA PnP (place) | performance: 36.94 -> 36.94 | No clear effect |
| add sub-tree expansion to parent trajectory sampling (ablation) | TDP · AntMaze Multi-goal Exploration | timesteps per goal: 574.3 -> 558.4 | Helped |
| add particle guidance to parent branching (ablation) | TDP · AntMaze Multi-goal Exploration | number of found goals: 64.6 -> 66.1 | Helped |
| increase fast denoising steps from 50 to 400 (ablation) | TDP · PnWP | performance: 65.7 { $\pm$ 0.14} -> 68.8 { $\pm$ 0.10} | Helped |
| replace fixed particle guidance potential with a learned potential (ablation) | TDP · PnP (stack) | performance: 61.17 { $\pm$ 0.24} -> 61.28 { $\pm$ 0.22} | No clear effect |
| increase particle guidance scale from 0.5 to 1.0 (ablation) | TDP · PnWP | performance: 67.1 { $\pm$ 0.10} -> 64.8 { $\pm$ 0.13} | Hurt |
| increase gradient guidance scale from 100 to 200 (ablation) | TDP · PnWP | performance: 67.1 { $\pm$ 0.10} -> 64.0 { $\pm$ 0.14} | Hurt |
Surprising findings
- Learned particle guidance gives only marginal gains over fixed particle guidance (e.g., PnWP 67.23 vs 66.81), so the fixed potential is nearly as good.
- Conditional particle guidance in parent branching can bias samples toward local optima, which hurts performance without sub-tree expansion.
Limitations
- Bi-level sampling adds computational cost from pairwise trajectory distance computation and extra fast denoising.
- Gradient guidance strength alpha_g must still be tuned per task.
- Maze2D gold-picking uses an approximate distance guide for gradient guidance, with the true guide used only for selection.
Experimental setup
Datasets: Maze2D PDDLStream block stacking demonstrations AntMaze
Benchmarks: Maze2D gold-picking KUKA PnP (stack) KUKA PnP (place) KUKA PnWP AntMaze multi-goal exploration
Metrics: mean performance score number of found goals sequence match score timesteps per goal
Baselines: Diffuser Diffuser-gamma (TAT) AdaptDiffuser MCSS MCSS+SS TDP w/o child TDP w/o PG
Builds on: Diffuser particle guidance Trajectory Aggregation Tree Monte Carlo tree diffusion classifier guidance
Closest papers by meaning
- Task-Agnostic Pre-training and Task-Guided Fine-tuning for Versatile Diffusion Planner (ICML 2025 · similarity 0.89)
- Diffusion-ES: Gradient-free Planning with Diffusion for Autonomous and Instruction-guided Driving (CVPR 2024 · similarity 0.89)
- Resisting Stochastic Risks in Diffusion Planners with the Trajectory Aggregation Tree (ICML 2024 · similarity 0.88)
- Prior-Guided Diffusion Planning for Offline Reinforcement Learning (NeurIPS 2025 · similarity 0.87)
- Compositional Monte Carlo Tree Diffusion for Extendable Planning (NeurIPS 2025 · similarity 0.87)
- Fast Monte Carlo Tree Diffusion: 100× Speedup via Parallel and Sparse Planning (NeurIPS 2025 · similarity 0.87)
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