Create Skills with Rewards Using the SDK

The Composabl SDK offers a suite of advanced tools to train skills using deep reinforcement learning. Using the Python teacher class, you can fine-tune the rewards for your skills. Once you have configured a skill with the SDK, you can publish it to the UI to use in agent designs.

Create a New Skill

To create a skill in the Python SDK, begin by logging in to the SDK by typing Composabl login from the CLI.

Then type composabl skill new.

Give the skill a name and a description in response to the prompts that follow. Choose whether your skill should be a teacher (learned with AI), controller (a programmed module like an optimization algorithm or MPC controller), or coach.

Specify the folder where you’d like to create the skill.

The Composal SDK will create a folder and Python teacher file from the template.

The Python Teacher Class

The Python teacher class offers several functions that you can use to fine-tune the training of your skills.

Functions for Training

Train with Rewards: the compute_reward Function

The compute_reward function provides the bulk of the feedback after each agent action about how much that action contributed to the success of the skill. This function returns a number that represents the reward signal the agent will receive for its last decision. Reward functions, as they are called in reinforcement learning, can be tricky to craft. Learn more about how to write good reward functions.

python
def compute_reward(self, transformed_sensors, action, sim_reward):
        self.counter += 1
        if self.past_ sensors is None:
            self.past_ sensors = transformed_ sensors
            return 0
        else:
            if self.past_ sensors ["state1"] < transformed_ sensors ["state1"]:
                return 1
            else:
                return -1

End Training: the compute_termination Function​

The compute_termination function tells the Composabl platform when to terminate a practice episode and start over with a new practice scenario (episode). From a teaching perspective, it makes most senses to terminate an episode when the agent succeeds, fails, or is pursuing a course of action that you do not find likely to succeed. This function returns a Boolean flag (True or False) whether to terminate the episode. You can calculate this criteria however seems best.

python
def compute_termination(self, transformed_ sensors, action):
        return False

Define Success: the compute_success_criteria Function​

The success_criteria function provides a definition of skill success and a proxy for how completely the agent has learned the skill. The platform uses the output of this function (True or False) to calculate when to stop training one skill and move on to training the next skill. It is also used to determine when to move to the next skill in a fixed order sequence. The agent cannot move from one skill in a fixed order sequence to the next, until the success criteria for one skill is reached.

python
def compute_success_criteria(self, transformed_ sensors, action):
        return self.counter > 100

Here are some examples of success criteria definition:

• A simple but naive success criteria might return True if the average reward for an episode or scenario crosses a threshold, but False if it does not.

• A more complex success criteria might calculate root mean squared error (RMSE) for key variables across the episode and return True if the error is less than a customer specified benchmark, but False otherwise.

• A complex success criteria might compare a benchmark controller or another agent to the agent across many key variables and trials. It returns True if the agent beats the benchmark on this criteria, but False otherwise.

Train with Goals

Training with goals lets you use a predefined reward structure rather than configuring the rewards individually. When you use a goal, your agent will inherit the compute reward, compute termination, and compute success functions from the goal. (You will still have the option to further customize those functions as needed.)

The five goal types you can use are:

• AvoidGoal

• MaximizeGoal

• MinimizeGoal

• ApproachGoal

• MaintainGoal

These have the same parameters and work the same way as the goal types in the UI.

Goals are added using specialized teacher classes rather than the general teacher class that you would otherwise use to teach skills. For example, for a skill named Balance that you wanted to train with a goal to maintain a specific orientation, you would use the MaintainGoal teacher class.

python
class BalanceTeacher(MaintainGoal):
	def __init__(self, *args, **kwargs):
super(),__init__(“pole_theta”, “Maintain pole to upright”, target=0, stop_distance=0.418)

The parameters you can use for goals are:

You can also use more than one goal for a single skill using the CoordinatedGoal teacher class. This is useful when your agent needs to behave in a way that creates a balance between two goals that are both important.

Functions to Guide Agent Behavior with Rules

Just like rules guide training and behavior for humans, providing rules for the agent to follow can guide agent decision-making more quickly to success. Rules guide the behavior of an agent based on expertise and constraints.

Add Rules: the compute_action_mask Function

The compute_action_mask teaching function expresses rules that trainable agents must follow.

python
 # The action mask provides rules at each step about which actions the agent is allowed to take.
    def compute_action_mask(self, transformed_ sensors, action):
        return [0, 1, 1]

The compute_action_mask teaching function works only for discrete action spaces (where the actions are integers or categories), not for continuous action spaces (where decision actions are decimal numbers). If you specify a mask for a skill whose actions are continuous, the platform will ignore the action mask.

The function returns a list of 0 and 1 values. Zero means that the action is forbidden by the rule. One means that the action is allowed by the rule. The function may change returned value after each decision. This allows complex logic to express nuanced rules.

In the example above, the first action is forbidden for the next decision, but the second and third actions are allowed. The logic in the skill itself (whether learned or programmed) will choose between the allowed second and third actions.

All selectors have a discrete action space (they choose which child skill to activate), so you can always apply the compute_action_mask function to teach them.

Functions to Manage Information Inside Agents

As information passes through perceptors, skills, and selectors in the agent, sometimes it needs to change format along the way. You can use three teaching functions to transform sensor and action variables inside agents: transform_ sensors, transform_action, and filtered_ sensor _space.

Transform Sensor Variables: the transform_sensors function​

To transform sensor variables, use the transform_sensor function to calculate changes to specific sensors, then return the complete set of sensor variables (the observation space).

python
def transform_sensor(self, sensor, action):
        return sensor

Two of the most common reasons for transforming sensor variables are conversion and normalization. For example, if a simulator reports temperature values in Fahrenheit, but the agent expects temperature values in Celsius, use the transform_sensor function to convert between the two.

Normalization is when you transform variables into different ranges. For example, one sensor variable in your agent might have very large values (in the thousands), but another variable might have small values (in the tenths), so you might use the transform_sensor function to transform these disparate sensor values to a range from 0 to 1 so that they can better be compared and used in the agent.

Transform Decisions within the Agent​: the transform_action function​

You may want to transform action variables for the same reasons as sensor variables.

python
def transform_action(self, transformed_sensor, action):
    return action

Filter the Sensor List: the filtered_sensor_space function​

Use the filtered_sensor_space function to pare down the list of sensor variables you need for a particular skill. Pass only the information that a skill or module needs in order to learn or perform well.

python
def filtered_sensor_space(self):
        return ["state1"]
Return a list of all the sensor variables that you want passed to the skill by this teacher.