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

Learning Brains

The Learning Brain works differently if you are training it or not. When used in an environment connected to Python, the Python process will train the Brain. If no Python Process exists, the Learning Brain will use its pre-trained model.

Training Mode / External Control

When running an ML-Agents training algorithm, at least one Brain asset must be in the Academy's Broadcast Hub. This allows the training process to collect the observations of Agents using that Brain and give the Agents their actions.

In addition to using a Learning Brain for training using the ML-Agents learning algorithms, you can use a Learning Brain to control Agents in a Unity environment using an external Python program. See Python API for more information.

Inference Mode / Internal Control

When not training, the Learning Brain uses a TensorFlow model to make decisions. The Proximal Policy Optimization (PPO) and Behavioral Cloning algorithms included with the ML-Agents SDK produce trained TensorFlow models that you can use with the Learning Brain type.

A model is a mathematical relationship mapping an agent's observations to its actions. TensorFlow is a software library for performing numerical computation through data flow graphs. A TensorFlow model, then, defines the mathematical relationship between your Agent's observations and its actions using a TensorFlow data flow graph.

Creating a graph model

The training algorithms included in the ML-Agents SDK produce TensorFlow graph models as the end result of the training process. See Training ML-Agents for instructions on how to train a model.

Using a graph model

To use a graph model:

1. Select the Learning Brain asset in the Project window of the Unity Editor.

2. Import the model_name file produced by the PPO training program. (Where model_name is the name of the model file, which is constructed from the name of your Unity environment executable and the run-id value you assigned when running the training process.)

   You can import assets into Unity in various ways. The easiest way is to simply drag the file into the Project window and drop it into an appropriate folder.

3. Once the model_name.nn file is imported, drag it from the Project window to the Model field of the Brain component.

If you are using a model produced by the ML-Agents mlagents-learn command, use the default values for the other Learning Brain parameters.

Learning Brain properties

The default values of the TensorFlow graph parameters work with the model produced by the PPO and BC training code in the ML-Agents SDK. To use a default ML-Agents model, the only parameter that you need to set is the Model, which must be set to the .nn file containing the trained model itself.

• Model : This must be the .nn file corresponding to the pre-trained TensorFlow graph. (You must first drag this file into your Project window and then from the Resources folder into the inspector)