ml-agents/docs/Learning-Environment-Design-Player-Brains.md

Player Brain

The Player Brain type allows you to control an Agent using keyboard commands. You can use Player Brains to control a "teacher" Agent that trains other Agents during imitation learning. You can also use Player Brains to test your Agents and environment before changing their Brain types to External and running the training process.

Player Brain properties

The Player Brain properties allow you to assign one or more keyboard keys to each action and a unique value to send when a key is pressed.

Note the differences between the discrete and continuous action spaces. When a Brain uses the discrete action space, you can send one integer value as the action per step. In contrast, when a Brain uses the continuous action space you can send any number of floating point values (up to the Vector Action Space Size setting).

Property		Description
Continuous Player Actions		The mapping for the continuous vector action
space. Shown when the action space is Continuous	.
	Size	The number of key commands defined. You can assign more than one
command to the same action index in order to send different values for that
action. (If you press both keys at the same time, deterministic results are not guaranteed.)
	Element 0–N	The mapping of keys to action values.
	Key	The key on the keyboard.
	Index	The element of the Agent's action vector to set when this key is
pressed. The index value cannot exceed the size of the Action Space (minus 1,
since it is an array index).
	Value	The value to send to the Agent as its action for the specified
index when the mapped key is pressed. All other members of the action vector
are set to 0.
Discrete Player Actions		The mapping for the discrete vector action space.
Shown when the action space is Discrete.
	Size	The number of key commands defined.
	Element 0–N	The mapping of keys to action values.
	Key	The key on the keyboard.
	Branch Index	The element of the Agent's action vector to set when this
key is pressed. The index value cannot exceed the size of the Action Space
(minus 1, since it is an array index).
	Value	The value to send to the Agent as its action when the mapped key
is pressed. Cannot exceed the max value for the associated branch (minus 1,
since it is an array index).

For more information about the Unity input system, see Input.