Johnny Fernandes
97 lines
3.6 KiB
Markdown
97 lines
3.6 KiB
Markdown
# Training pipeline
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Behavior cloning of analytic herding teachers into a neural network
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policy that runs in Webots. PPO from scratch and PPO fine-tune of BC
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were tried earlier and are kept under `train_ppo.py` as experimental
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options, but the BC route alone is what we ship.
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## Files
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```
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herding_env.py — Gymnasium env (used for demo collection + eval)
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bc_pretrain.py — supervised MSE+cosine training of an SB3 MlpPolicy
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against (obs, action) demos
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eval.py — analytic teachers + BC policies, full n=1..10 grid
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parity_test.py — shape/determinism/baseline smoke test
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train_ppo.py — PPO trainer (experimental — see Appendix below)
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configs/ — PPO hyperparameter YAML
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runs/ — checkpoints (.gitignored)
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```
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## Setup
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```
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pip install -r requirements.txt
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```
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CPU is the default and recommended device — SB3 PPO with an MLP policy
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of this size runs faster on CPU than GPU because the bottleneck is
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rollout collection, not gradient compute.
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## The BC pipeline
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```
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# 1. Generate demos from an analytic teacher.
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# --teacher: strombom (default), sequential, drive_only, hybrid, strombom_smooth
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python -m tools.collect_demos --teacher strombom \
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--out demos.npz --seeds-per-n 30 --subsample 3
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# 2. Behavior-clone the demos into an MLP policy.
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python -m training.bc_pretrain --demos demos.npz \
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--out runs/bc_flock --epochs 100 --net-arch 512,512
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# 3. Evaluate the resulting policy.
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python -m training.eval --policy runs/bc_flock \
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--max-flock 10 --max-steps 30000 --n-seeds 5
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```
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Wall time: ~10 min demos + ~5 min BC training + ~5 min eval.
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`bc_pretrain.py` saves the **best-val_cos** snapshot, not the final
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epoch — multi-modal teachers (Strömbom's collect/drive switch) make
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training noisy and the last epoch is often worse than an earlier one.
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## Available analytic teachers
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| Name | What it does | Best for |
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| `strombom` | Canonical Strömbom — collect when flock is scattered, drive CoM otherwise | Tight-cohesion regime, n=1-10 |
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| `sequential` | Pick the sheep closest to the pen and drive only it | Loose-cohesion regime, n=1-10 |
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| `drive_only` | Strömbom drive without collect mode (continuous action) | Easier-to-BC alternative; less reliable than full Strömbom |
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| `hybrid` | Drive rearmost sheep when far, switch to closest near gate | Failed experiment, kept for write-up |
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| `strombom_smooth` | Sigmoid-blended Strömbom collect↔drive | Failed experiment |
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## Evaluating the analytic teachers directly
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```
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python -m training.eval --policy strombom --max-flock 10 --max-steps 30000 --n-seeds 5
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python -m training.eval --policy sequential --max-flock 10 --max-steps 30000 --n-seeds 5
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```
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## Webots inference
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The Webots dog controller (`controllers/shepherd_dog/shepherd_dog.py`)
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loads a saved BC zip when launched in `rl` mode:
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```
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HERDING_POLICY_DIR=$PWD/runs/bc_flock tools/run_webots.sh 10 rl
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```
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It auto-discovers a checkpoint named `policy.zip`, `best_model.zip`, or
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`final.zip` in the directory.
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## Appendix — experimental PPO scripts
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`train_ppo.py` contains the PPO/RL pipeline tried before BC:
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* PPO from scratch with curriculum learning over flock size + spawn area.
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* PPO fine-tune of a BC checkpoint.
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Both ran into stability issues (PPO's exploration noise destroys BC
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weights faster than the reward signal can rebuild them; PPO from
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scratch never sees pen events often enough during random exploration to
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credit-assign the +500 done bonus).
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The script is left in place because the abstractions are sound and the
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code is reusable for follow-up work (e.g. KL-regularised fine-tune
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with a frozen reference policy). Not part of the deliverable pipeline.
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