Methods, systems and apparatus, including computer programs encoded on computer storage media, for training a value neural network that is configured to receive an observation characterizing a state of an environment being interacted with by an agent and to process the observation in accordance with parameters of the value neural network to generate a value score. One of the systems performs operations that include training a supervised learning policy neural network; initializing initial values of parameters of a reinforcement learning policy neural network having a same architecture as the supervised learning policy network to the trained values of the parameters of the supervised learning policy neural network; training the reinforcement learning policy neural network on second training data; and training the value neural network to generate a value score for the state of the environment that represents a predicted long-term reward resulting from the environment being in the state.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A neural network training system comprising one or more computers and one or more storage devices storing instructions that when executed by the one or more computers cause the one or more computers to perform operations for training a value neural network that is configured to receive an observation characterizing a state of an environment being interacted with by an agent and to process the observation in accordance with parameters of the value neural network to generate a value score, the operations comprising: training a supervised learning policy neural network, wherein the supervised learning policy neural network is configured to receive the observation and to process the observation in accordance with parameters of the supervised learning policy neural network to generate a respective action probability for each action in a set of possible actions that can be performed by the agent to interact with the environment, and wherein training the supervised learning policy neural network comprises training the supervised learning policy neural network on labeled training data using supervised learning to determine trained values of the parameters of the supervised learning policy neural network; initializing initial values of parameters of a reinforcement learning policy neural network having a same architecture as the supervised learning policy network to the trained values of the parameters of the supervised learning policy neural network; training the reinforcement learning policy neural network on second training data generated from interactions of the agent with a simulated version of the environment using reinforcement learning to determine trained values of the parameters of the reinforcement learning policy neural network from the initial values; and training the value neural network to generate a value score for the state of the environment that represents a predicted long-term reward resulting from the environment being in the state by training the value neural network on third training data generated from interactions of the agent with the simulated version of the environment using supervised learning to determine trained values of the parameters of the value neural network from initial values of the parameters of the value neural network. 2. The system of claim 1, wherein the environment is a real-world environment, and wherein the actions in the set of actions are possible control inputs to control the interaction of the agent with the environment. 3. The system of claim 2, wherein the environment is a real-world environment, wherein the agent is a control system for an autonomous or semi-autonomous vehicle navigating through the real-world environment, wherein the actions in the set of actions are possible control inputs to control the autonomous or semi-autonomous vehicle, and wherein the simulated version of the environment is a motion simulation environment that simulates navigation through the real-world environment. 4. The system of claim 2, wherein the predicted long-term reward received by the agent reflects a predicted degree to which objectives for the navigation of the vehicle through the real-world environment will be satisfied as a result of the environment being in the state. 5. The system of claim 1, wherein the environment is a patient diagnosis environment, wherein the observation characterizes a patient state of a patient, wherein the agent is a computer system for suggesting treatment for the patient, wherein the actions in the set of actions are possible medical treatments for the patient, and wherein the simulated version of the environment is a patient health simulation that simulates effects of medical treatments on patients. 6. The system of claim 1, wherein the environment is a protein folding environment, wherein the observation characterizes a current state of a protein chain, wherein the agent is a computer system for determining how to fold the protein chain, wherein the actions are possible folding actions for folding the protein chain, and wherein the simulated version of the environment is a simulated protein folding environment that simulates effects of folding actions on protein chains. 7. The system of claim 1, wherein the environment is a virtualized environment in which a user competes against a computerized agent to accomplish a goal, wherein the agent is the computerized agent, wherein the actions in the set of actions are possible actions that can be performed by the computerized agent in the virtualized environment, and wherein the simulated version of the environment is a simulation in which the user is replaced by another computerized agent. 8. The system of claim 1, wherein training the reinforcement learning policy neural network on the second training data comprises selecting actions to be performed by the agent while interacting with the simulated version of the environment using the reinforcement learning policy neural network. 9. The system of claim 1, wherein training the reinforcement learning policy network on the second training data comprises: training the reinforcement learning policy network to generate action probabilities that represent, for each action, a predicted likelihood that the long-term reward will be maximized if the action is performed by the agent in response to the observation instead of any other action in the set of possible actions. 10. The system of claim 1, wherein the labeled training data comprises a plurality of training observations and, for each training observation, an action label, wherein each training observation characterizes a respective training state, and wherein the action label for each training observation identifies an action that was performed in response to the training observation. 11. The system of claim 10, wherein training the supervised learning policy neural network on the labeled training data comprises: training the supervised learning policy neural network to generate action probabilities that match the action labels for the raining observations. 12. The system of claim 1, the operations further comprising: training a fast rollout policy neural network on the labeled training data, wherein the fast rollout policy neural network is configured to receive a rollout input characterizing the state and to process the rollout input to generate a respective rollout action probability for each action in the set of possible actions, and wherein a processing time necessary for the fast rollout policy neural network to generate the rollout action probabilities is less than a processing time necessary for the supervised learning policy neural network to generate the action probabilities. 13. The system of claim 12, wherein the rollout input characterizing the state contains less data than the observation characterizing the state. 14. The system of claim 12, the operations further comprising: using the fast rollout policy neural network to evaluate states of the environment as part of searching a state tree of states of the environment, wherein the state tree is used to select actions to be performed by the agent in response to received observations. 15. The system of claim 1, the operations further comprising: using the trained value function neural network to evaluate states of the environment as part of searching a state tree of states of the environment, wherein the state tree is used to select actions to be performed by the agent in response to received observations. 16. A method of training a value neural network that is configured to receive an observation characterizing a state of an environment being interacted with by an agent and to process the observation in accordance with parameters of the value neural network to generate a value score, the method comprising: training a supervised learning policy neural network, wherein the supervised learning policy neural network is configured to receive the observation and to process the observation in accordance with parameters of the supervised learning policy neural network to generate a respective action probability for each action in a set of possible actions that can be performed by the agent to interact with the environment, and wherein training the supervised learning policy neural network comprises training the supervised learning policy neural network on labeled training data using supervised learning to determine trained values of the parameters of the supervised learning policy neural network; initializing initial values of parameters of a reinforcement learning policy neural network having a same architecture as the supervised learning policy network to the trained values of the parameters of the supervised learning policy neural network; training the reinforcement learning policy neural network on second training data generated from interactions of the agent with a simulated version of the environment using reinforcement learning to determine trained values of the parameters of the reinforcement learning policy neural network from the initial values; and training the value neural network to generate a value score for the state of the environment that represents a predicted long-term reward resulting from the environment being in the state by training the value neural network on third training data generated from interactions of the agent with the simulated version of the environment using supervised learning to determine trained values of the parameters of the value neural network from initial values of the parameters of the value neural network. 17. The method of claim 16, wherein training the reinforcement learning policy neural network on the second training data comprises selecting actions to be performed by the agent while interacting with the simulated version of the environment using the reinforcement learning policy neural network. 18. The method of claim 16, wherein training the reinforcement learning policy network on the second training data comprises: training the reinforcement learning policy network to generate action probabilities that represent, for each action, a predicted likelihood that the long-term reward will be maximized if the action is performed by the agent in response to the observation instead of any other action in the set of possible actions. 19. The method of claim 16, wherein the labeled training data comprises a plurality of training observations and, for each training observation, an action label, wherein each training observation characterizes a respective training state, and wherein the action label for each training observation identifies an action that was performed in response to the training observation. 20. One or more non-transitory computer storage media storing instructions that when executed by one or more computers cause the one or more computers to perform operations for training a value neural network that is configured to receive an observation characterizing a state of an environment being interacted with by an agent and to process the observation in accordance with parameters of the value neural network to generate a value score, the operations comprising: training a supervised learning policy neural network, wherein the supervised learning policy neural network is configured to receive the observation and to process the observation in accordance with parameters of the supervised learning policy neural network to generate a respective action probability for each action in a set of possible actions that can be performed by the agent to interact with the environment, and wherein training the supervised learning policy neural network comprises training the supervised learning policy neural network on labeled training data using supervised learning to determine trained values of the parameters of the supervised learning policy neural network; initializing initial values of parameters of a reinforcement learning policy neural network having a same architecture as the supervised learning policy network to the trained values of the parameters of the supervised learning policy neural network; training the reinforcement learning policy neural network on second training data generated from interactions of the agent with a simulated version of the environment using reinforcement learning to determine trained values of the parameters of the reinforcement learning policy neural network from the initial values; and training the value neural network to generate a value score for the state of the environment that represents a predicted long-term reward resulting from the environment being in the state by training the value neural network on third training data generated from interactions of the agent with the simulated version of the environment using supervised learning to determine trained values of the parameters of the value neural network from initial values of the parameters of the value neural network.