README.md

Population-Based Training

This is a Python implementation of population-based training, as described in Population Based Training of Neural Networks by Jaderberg et al.

Example training run: Evaluation metric (top) and hyperparameter values (bottom) over time during population-based training (population size 10).

Usage

Clone this repository and add it to your project's source tree. Then add PBT to your project with the following commands:

1. Start a PBT server.

   server = PBTServer(args.port, args.auth_key, args.maximize_metric)

2. Create a PBT client:

   pbt_client = PBTClient(args.pbt_server_url, args.pbt_server_port, args.pbt_server_key, args.pbt_config_path)

3. Exploit and explore: Suppose we've just written a checkpoint to ckpt_path and evaluated our model, producing a score metric_val (e.g., validation accuracy). Then we might do the following:

   pbt_client.save(ckpt_path, metric_val)
   if pbt_client.should_exploit():
       # Exploit
       pbt_client.exploit()
   
       # Load model and optimizer parameters from exploited network
       model = load_model(pbt_client.parameters_path(), args.gpu_ids)
       model.train()
       load_optimizer(pbt_client.parameters_path(), gpu_ids, optimizer)
   
       # Explore
       pbt_client.explore()

   Note each step performed in the block above:

   1. pbt_client.save: Tell the PBT server that this client just saved a checkpoint to ckpt_path with evaluation score metric_val.
   2. pbt_client.should_exploit: Ask the PBT server if this client should exploit another model. E.g., when using truncation selection, this is true when the client's performance ranks in the bottom 20% of the population.
   3. pbt_client.exploit: Ask the PBT server for a checkpoint path of a model to exploit.
   4. load_model and load_optimizer: Load the parameters and hyperparameters of the exploited model.
   5. pbt_client.explore: Explore the hyperparameter space. E.g., when using the perturb strategy, multiply each hyperparameter by 0.8 or 1.2.