Monty.Frameworks.Models.MotorPolicies (ExTbpMonty.Core v0.1.0)

Policies: how a body decides what to do with the space it is in.

Mirrors tbp/monty/frameworks/models/motor_policies.py, the largest file in Monty's motor system. Ported so far:

...MotorPolicies.NoGoalProvided — ported: raised when a policy needs a goal and was given none;
...MotorPolicies.SurfacePolicyTelemetry — ported: why a surface policy chose what it chose;
...MotorPolicies.PolicyStatus — ported: :ready or :in_progress;
...MotorPolicies.MotorPolicyResult — ported: what one call decided;
...MotorPolicies.RuntimeMotorPolicy and ...MotorPolicies.MotorPolicy — ported: the two interfaces, the second a policy that can also be reset;
...MotorPolicies.BasePolicy — ported: one sampled action, whatever the step looked like;
...MotorPolicies.InformedPolicy — ported: sample while the sensor is on the object, step back while it is not, and jump to a goal when one arrives;
...MotorPolicies.SurfacePolicy — ported: walk the surface of an object, and search for it when it is lost;
...MotorPolicies.NaiveScanPolicy — ported: scan the object in a square spiral, one leg longer each time;
...MotorPolicies.InformedPolicyRandomWalk — ported: InformedPolicy's walk without the rest of it, which is the default the distant configs give their selector;
...MotorPolicies.PredefinedPolicy — ported: replay the actions written in a JSON file, cycled for ever;
...MotorPolicies.JumpToGoal — ported: teleport to a goal, and undo the teleport when it lands somewhere useless;
undo_last_action/1 — ported: the module-level function — Monty calls it fixme_undo_last_action — that turns an action into its opposite.

Still planned: nothing — every class in Monty's motor_policies.py is ported. DistantPolicySelector, the distant agent's selector, is ported under Monty.Frameworks.Models.MotorPolicySelectors.

A policy here is a struct plus the module named after it, so a policy can be stored in a selector as a value and stepped without a process — the same shape as Monty.Frameworks.Models.ObjectModel and the goal generators.

Summary

Functions

depth_at_center(observations, agent_id, sensor_id)

The depth at the centre pixel of a sensor's view.

enforce_pi_bounds(theta)

The same angle, brought back between -π and π.

from_config(config)

The policy a config describes.

projected_angle_from_vec(list)

The orientation a direction in the agent's plane points in, in radians.

projected_vec_from_angle(angle)

The direction in the agent's plane that an orientation points in.

successful_jump(policy)

Ask a policy what it does now that a jump has landed.

theta_change(a, b)

The signed change from one orientation to another, in radians.

undo_last_action(action)

The action that would undo action.

Functions

depth_at_center(observations, agent_id, sensor_id)

@spec depth_at_center(map(), atom() | String.t(), String.t()) :: float()

The depth at the centre pixel of a sensor's view.

Monty's PositioningProcedure.depth_at_center, a static method of the positioning protocol; the function lives with the procedures now and this is a delegation, so a policy can ask the question without reaching into the environment layer (docs/monty-differences.md §2.7).

enforce_pi_bounds(theta)

@spec enforce_pi_bounds(float()) :: float()

The same angle, brought back between -π and π.

Monty's enforce_pi_bounds, as a loop of ±2π: a plain rem/2 would do it in one step, but the loop is what the angles' meaning in Monty is, and it is what the port follows.

from_config(config)

@spec from_config(map()) :: Monty.Frameworks.Models.MotorPolicies.MotorPolicy.t()

The policy a config describes.

policy:
  _target_: tbp.monty.frameworks.models.motor_policies.SurfacePolicyCurvatureInformed
  agent_id: agent_id_0
  alpha: 0.1
  action_sampler:
    _target_: ...ConstantSampler

The class decides which parameters are required: each policy's own new/1 fetches what it cannot do without, so a config that leaves one out fails here rather than at the first step of the episode.

projected_angle_from_vec(list)

@spec projected_angle_from_vec(Monty.Geometry.Rotation.vector()) :: float()

The orientation a direction in the agent's plane points in, in radians.

Monty's projected_angle_from_vec: atan2(x, y), in that order, because theta of zero means "along +y" — up in the agent's frame — rather than "along +x".

projected_vec_from_angle(angle)

@spec projected_vec_from_angle(float()) :: Monty.Geometry.Rotation.vector()

The direction in the agent's plane that an orientation points in.

Monty's projected_vec_from_angle. The quarter-turn offsets on cos and sin are what put theta of zero on +y and keep a tangential step in the plane.

successful_jump(policy)

@spec successful_jump(struct()) :: struct()

Ask a policy what it does now that a jump has landed.

Monty calls self._handle_successful_jump(), which a subclass overrides; here the struct's module is asked instead (docs/monty-differences.md §2.9).

theta_change(a, b)

@spec theta_change(float(), float()) :: float()

The signed change from one orientation to another, in radians.

Monty's theta_change: a plain subtraction with the loop-around corrected, so that 0 to 3π/2 is a quarter turn back rather than three quarters forward.

undo_last_action(action)

@spec undo_last_action(Monty.Frameworks.Actions.Action.t()) ::
  Monty.Frameworks.Actions.Action.t()

The action that would undo action.

Mirrors fixme_undo_last_action. Only the six actions an informed policy samples can be undone, and each is undone by itself with its amount negated — a LookDown is undone by a LookDown of the opposite rotation, not by a LookUp, because the policy is reversing a move it made rather than commanding the agent. MoveTangentially keeps its direction and negates its distance, which is what Monty's comment on that line says.

Monty's fixme_ prefix is the project saying it would rather have Action.undo; the name here leaves the complaint out and the doc keeps it. Monty raises TypeError for anything else and so does this, as an ArgumentError: a policy configured with an action it cannot undo has nothing sensible to do with a percept that left the object. That is docs/monty-differences.md §2.8, along with the rest of the vocabulary differences.