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Simple Hierarchical Planning with Diffusion
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Proposes Hierarchical Diffuser, which trains a high-level Sparse Diffuser on every-K-th-state subgoal trajectories and a low-level Diffuser on segments between subgoals, enabling faster and better diffusion-based offline planning.
Problem
Diffuser-style diffusion planners are computationally expensive for long horizons, sample inefficient, and their plans cover the dataset distribution poorly, and they generalize poorly on compositional out-of-distribution tasks.
Approach
Repurpose Diffuser at two levels: a high-level "jumpy" diffuser models subsampled subgoal trajectories (every K-th state, optionally with dense actions) for a larger effective receptive field at lower cost, and a low-level diffuser plans dense segments between adjacent subgoals, with both trained in parallel and low-level plans generated concurrently.
Key results
- HD achieves 139.9 average on single-task Maze2D vs 119.5 for Diffuser and 123.5 for HDMI, and 88.8 average on AntMaze vs 36.0 for Diffuser.
- HD-DA reaches 84.6 average on Gym-MuJoCo vs 77.5 for Diffuser, and 72.5 vs 53.1 average on FrankaKitchen.
- On the compositional OOD task, HD achieves 100% success while all Diffuser kernel-size variants achieve 0%; planning time is about 10x faster than Diffuser on medium and large mazes.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| replace flat Diffuser planning with hierarchical planning | Diffuser · Maze2D Single-task Average | score: 119.5 -> 139.9 | Helped |
| replace flat Diffuser planning with hierarchical planning | Diffuser · Multi2D Multi-task Average | score: 129.4 -> 149.9 | Helped |
| replace flat Diffuser planning with hierarchical planning | Diffuser · AntMaze Average | score: 36.0 -> 88.8 | Helped |
| use Sparse Diffuser as a standalone planner (ablation) | Diffuser · Maze2D Single-task Average | score: 119.5 -> 133.4 | Helped |
| add low-level refinement to Sparse Diffuser (ablation) | Sparse Diffuser · Maze2D Single-task Average | score: 133.4 -> 139.9 | Helped |
| use Sparse Diffuser as a standalone planner (ablation) | Diffuser · Multi2D Multi-task Average | score: 129.4 -> 145.8 | Helped |
| add low-level refinement to Sparse Diffuser (ablation) | Sparse Diffuser · Multi2D Multi-task Average | score: 145.8 -> 149.9 | Helped |
| include dense actions in the high-level planner (ablation) | HD · Gym-MuJoCo Medium-Replay Walker2d | score: 77.2 -> 84.1 | Helped |
| include dense actions in the high-level planner (ablation) | HD · Gym-MuJoCo Medium-Replay HalfCheetah | score: 37.5 -> 38.1 | Helped |
| increase the jumpy step from K=4 to K=8 (ablation) | HD · Gym-MuJoCo Average | score: 84.6 -> 81.8 | Hurt |
| increase the jumpy step from K=15 to K=21 (ablation) | HD · Maze2D Single-task Average | score: 139.9 -> 137.7 | Hurt |
| increase the jumpy step from K=15 to K=21 (ablation) | HD · Multi2D Multi-task Average | score: 149.9 -> 142.5 | Hurt |
Surprising findings
- Simply enlarging Diffuser's kernel size improves in-distribution performance but hurts compositional OOD generalization, with all Diffuser variants failing the OOD task.
- Including dense actions in the high-level subsampled trajectory improves guidance (return prediction) learning and RL performance in some environments.
Limitations
- Performance depends on dataset quality and coverage as an offline method.
- Fixed subgoal interval K is a task-dependent hyperparameter that may not suit complex real-world scenarios.
- Effectiveness depends on accuracy of the learned value function, which limits how large K can be.
Experimental setup
Datasets: D4RL Maze2D D4RL AntMaze D4RL Gym-MuJoCo D4RL FrankaKitchen Multi2D compositional OOD Maze2D (generated with PD controller)
Benchmarks: D4RL Maze2D D4RL AntMaze Multi2D D4RL Gym-MuJoCo D4RL FrankaKitchen compositional OOD Maze2D
Metrics: normalized return wall-clock training time wall-clock planning time success rate cosine similarity MSE
Baselines: Diffuser MPPI IQL IRIS HiGoC HDMI BC CQL DT TT MOReL BCQ
Builds on: Diffuser classifier guidance HDMI
Closest papers by meaning
- Structural Information-based Hierarchical Diffusion for Offline Reinforcement Learning (NeurIPS 2025 · similarity 0.90)
- Prior-Guided Diffusion Planning for Offline Reinforcement Learning (NeurIPS 2025 · similarity 0.90)
- State-Covering Trajectory Stitching for Diffusion Planners (NeurIPS 2025 · similarity 0.89)
- Diffusion Subgoal Planning for Long-Horizon Offline Goal-Conditioned Reinforcement Learning (NeurIPS 2026 · similarity 0.89)
- What Makes a Good Diffusion Planner for Decision Making? (ICLR 2025 · similarity 0.89)
- Task-Agnostic Pre-training and Task-Guided Fine-tuning for Versatile Diffusion Planner (ICML 2025 · similarity 0.89)
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