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Configure sweeps

A W&B Sweep combines a strategy for exploring hyperparameter values with the code that evaluates them. The strategy can be as simple as trying every option or as complex as Bayesian Optimization and Hyperband (BOHB).

Define a sweep configuration either in a Python dictionary or a YAML file. How you define your sweep configuration depends on how you want to manage your sweep.

info

Define your sweep configuration in a YAML file if you want to initialize a sweep and start a sweep agent from the command line. Define your sweep in a Python dictionary if you initialize a sweep and start a sweep entirely within a Python script or Jupyter notebook.

The following guide describes how to format your sweep configuration. See Sweep configuration options for a comprehensive list of top-level sweep configuration keys.

Basic structure​

Both sweep configuration format options (YAML and Python dictionary) utilize key-value pairs and nested structures.

Use top-level keys within your sweep configuration to define qualities of your sweep search such as the name of the sweep (name key), the parameters to search through (parameters key), the methodology to search the parameter space (method key), and more.

For example, the proceeding code snippets show the same sweep configuration defined within a YAML file and within a Python dictionary. Within the sweep configuration there are five top level keys specified: program, name, method, metric and parameters.

Define a sweep configuration in a YAML file if you want to manage sweeps interactively from the command line (CLI)

config.yaml
program: train.py
name: sweepdemo
method: bayes
metric:
  goal: minimize
  name: validation_loss
parameters:
  learning_rate:
    min: 0.0001
    max: 0.1
  batch_size:
    values: [16, 32, 64]
  epochs:
    values: [5, 10, 15]
  optimizer:
    values: ["adam", "sgd"]

Within the top level parameters key, the following keys are nested: learning_rate, batch_size, epoch, and optimizer. For each of the nested keys you specify, you can provide one or more values, a distribution, a probability, and more. For more information, see the parameters section in Sweep configuration options.

Double nested parameters​

Sweep configurations support nested parameters. To delineate a nested parameter, use an additional parameters key under the top level parameter name. Sweep configs support multi-level nesting.

Specify a probability distribution for your random variables if you use a Bayesian or random hyperparameter search. For each hyperparameter:

  1. Create a top level parameters key in your sweep config.
  2. Within the parameterskey, nest the following:
    1. Specify the name of hyperparameter you want to optimize.
    2. Specify the distribution you want to use for the distribution key. Nest the distribution key-value pair underneath the hyperparameter name.
    3. Specify one or more values to explore. The value (or values) should be inline with the distribution key.
      1. (Optional) Use an additional parameters key under the top level parameter name to delineate a nested parameter.
caution

Nested parameters defined in sweep configuration overwrite keys specified in a W&B run configuration.

For example, suppose you initialize a W&B run with the following configuration in a train.py Python script (see Lines 1-2). Next, you define a sweep configuration in a dictionary called sweep_configuration (see Lines 4-13). You then pass the sweep config dictionary to wandb.sweep to initialize a sweep config (see Line 16).

train.py
def main():
    run = wandb.init(config={"nested_param": {"manual_key": 1}})


sweep_configuration = {
    "top_level_param": 0,
    "nested_param": {
        "learning_rate": 0.01,
        "double_nested_param": {"x": 0.9, "y": 0.8},
    },
}

# Initialize sweep by passing in config.
sweep_id = wandb.sweep(sweep=sweep_configuration, project="<project>")

# Start sweep job.
wandb.agent(sweep_id, function=main, count=4)

The nested_param.manual_key that is passed when the W&B run is initialized (line 2) is not accessible. The run.config only possess the key-value pairs that are defined in the sweep configuration dictionary (lines 4-13).

Sweep configuration template​

The following template shows how you can configure parameters and specify search constraints. Replace hyperparameter_name with the name of your hyperparameter and any values enclosed in <>.

config.yaml
program: <insert>
method: <insert>
parameter:
  hyperparameter_name0:
    value: 0  
  hyperparameter_name1: 
    values: [0, 0, 0]
  hyperparameter_name: 
    distribution: <insert>
    value: <insert>
  hyperparameter_name2:  
    distribution: <insert>
    min: <insert>
    max: <insert>
    q: <insert>
  hyperparameter_name3: 
    distribution: <insert>
    values:
      - <list_of_values>
      - <list_of_values>
      - <list_of_values>
early_terminate:
  type: hyperband
  s: 0
  eta: 0
  max_iter: 0
command:
- ${Command macro}
- ${Command macro}
- ${Command macro}
- ${Command macro}

Sweep configuration examples​

config.yaml
program: train.py
method: random
metric:
  goal: minimize
  name: loss
parameters:
  batch_size:
    distribution: q_log_uniform_values
    max: 256 
    min: 32
    q: 8
  dropout: 
    values: [0.3, 0.4, 0.5]
  epochs:
    value: 1
  fc_layer_size: 
    values: [128, 256, 512]
  learning_rate:
    distribution: uniform
    max: 0.1
    min: 0
  optimizer:
    values: ["adam", "sgd"]

Bayes hyperband example​

program: train.py
method: bayes
metric:
  goal: minimize
  name: val_loss
parameters:
  dropout:
    values: [0.15, 0.2, 0.25, 0.3, 0.4]
  hidden_layer_size:
    values: [96, 128, 148]
  layer_1_size:
    values: [10, 12, 14, 16, 18, 20]
  layer_2_size:
    values: [24, 28, 32, 36, 40, 44]
  learn_rate:
    values: [0.001, 0.01, 0.003]
  decay:
    values: [1e-5, 1e-6, 1e-7]
  momentum:
    values: [0.8, 0.9, 0.95]
  epochs:
    value: 27
early_terminate:
  type: hyperband
  s: 2
  eta: 3
  max_iter: 27

The proceeding tabs show how to specify either a minimum or maximum number of iterations for early_terminate:

early_terminate:
  type: hyperband
  min_iter: 3

The brackets for this example are: [3, 3*eta, 3*eta*eta, 3*eta*eta*eta], which equals [3, 9, 27, 81].

Command example​

program: main.py
metric:
  name: val_loss
  goal: minimize

method: bayes
parameters:
  optimizer.config.learning_rate:
    min: !!float 1e-5
    max: 0.1
  experiment:
    values: [expt001, expt002]
  optimizer:
    values: [sgd, adagrad, adam]

command:
- ${env}
- ${interpreter}
- ${program}
- ${args_no_hyphens}
/usr/bin/env python train.py --param1=value1 --param2=value2

The proceeding tabs show how to specify common command macros:

Remove the {$interpreter} macro and provide a value explicitly to hardcode the python interpreter. For example, the following code snippet demonstrates how to do this:

command:
  - ${env}
  - python3
  - ${program}
  - ${args}
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