Lesson 14 of 21 in this unit
Predict actions from observations.
Train an imitation policy and diagnose closed-loop distribution shift.
By the end: Train an imitation policy and diagnose closed-loop distribution shift.
Prerequisites and path options
Why learn this? Learn how observation-conditioned action fitting differs from executing a safe and successful whole task.
Start with something concrete.
A student driver can match familiar steering demonstrations yet fail after drifting away from the road centre. Robot imitation has the same feedback problem.
Try the interactive modelWhat does low error on demonstrated actions establish?
Change one thing. Watch what follows.
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Understand what changed.
A shorter explanation, with the original worked examples available below. Both explain the same experiment and its limits.
The question
A student driver can match familiar steering demonstrations yet fail after drifting away from the road centre. Robot imitation has the same feedback problem.
Try it and inspect what changed
Train the policy, introduce a 0.3 m displacement and inspect its recovery.
Compare initial and trained policies at the same start and disturbance. Inspect the observation used for a poor action. Was that observation represented in collection? Add a recovery demonstration before claiming the architecture needs to be larger.
The calculation in words
The network receives six numbers: puck x/y, goal x/y and two instruction indicators. Eight tanh hidden units produce six tanh outputs: three planar commands. Training minimizes mean half-squared command error. Every gradient uses the same preceding checkpoint; the update rate is 0.6 and the interface performs at most five updates per action.
Keep the conclusion within the evidence
Our coordinates come directly from the rendered scene, so this is learned control from visual positions, not a learned image detector. The teacher is a proportional controller with saturation. Compare it directly with the network: a learned approximation is not automatically better than its teacher. Training only sees supplied and explicitly recorded training trajectories.
Repeated public development runs support debugging, not a final generalization claim. Four hundred updates is a work limit, not a convergence guarantee. A policy checkpoint does not authenticate how it was trained.
You can explore every lesson directly. Completing this page, submitting a project report and demonstrating understanding on a separate case are different records. Optional code is available in the robot-learning studio; it does not increase guided lesson completion requirements.
Open the full worked examples, calculations and limitations
This is the same reference used in Technical mode. Expand it whenever you need the exact numbers, assumptions or further explanation.
Start with the task
A student driver can match familiar steering demonstrations yet fail after drifting away from the road centre. Robot imitation has the same feedback problem.
Mechanism and units
The network receives six numbers: puck x/y, goal x/y and two instruction indicators. Eight tanh hidden units produce six tanh outputs: three planar commands. Training minimizes mean half-squared command error. Every gradient uses the same preceding checkpoint; the update rate is 0.6 and the interface performs at most five updates per action.
Our coordinates come directly from the rendered scene, so this is learned control from visual positions, not a learned image detector. The teacher is a proportional controller with saturation. Compare it directly with the network: a learned approximation is not automatically better than its teacher. Training only sees supplied and explicitly recorded training trajectories.
Work through the evidence
Compare initial and trained policies at the same start and disturbance. Inspect the observation used for a poor action. Was that observation represented in collection? Add a recovery demonstration before claiming the architecture needs to be larger.
Train the policy, introduce a 0.3 m displacement and inspect its recovery.
What this experiment can establish
Repeated public development runs support debugging, not a final generalization claim. Four hundred updates is a work limit, not a convergence guarantee. A policy checkpoint does not authenticate how it was trained.
Keep collection, fitting, frozen execution and interpretation as separate records. Save the configuration and complete result, including failures, in the robot-learning project. Report submission checks required evidence and text presence; reasoning and implementation quality need independent review.
A policy matches demonstration actions but fails after a push off its usual path. What comparison diagnoses this?
Take this idea with you.
Repeated public development runs support debugging, not a final generalization claim. Four hundred updates is a work limit, not a convergence guarantee. A policy checkpoint does not authenticate how it was trained.
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How this topic connects
Explore this topic on the interactive mapUse these connections to review a foundation or choose where to go next. You can open any topic without completing the others.
What it builds on
- Geometry and control
Prevent coordinate-frame mistakes when combining robot positions, sensor readings and targets.
Train an imitation policy and diagnose closed-loop distribution shift.
What it enables
- Robot-learning project Apply in a project
Combine demonstration provenance, policy comparisons and complete-task evidence in the robot-learning project; keep embodiment limits and review status explicit.