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Simple Ensemble

Ensemble methods are simple and effective ways to improve the performance of machine learning models. These methods combine the outputs of multiple models to create a stronger model. A simple ensemble takes the average of the predictions from multiple models without any weighting.

Formally, given a set of \(n\) models, each model \(f_i\) produces a prediction \(f_i(x)\) for an input \(x\). The final prediction \(F(x)\) of the simple ensemble is the unweighted average of the individual model predictions:

\[ F(x) = \frac{1}{n} \sum_{i=1}^n f_i(x) \]

This approach assumes that all models contribute equally to the final prediction and is particularly effective when the individual models have similar performance levels.

Examples

CLI Usage

Configuration template for the ensemble algorithm:

config/method/ensemble/simple_ensemble.yaml
# =============================================================================
# FusionBench Method Configuration: Simple Ensemble
# =============================================================================
# Averages model predictions uniformly.
#
# device_map: leave null for single device or provide a mapping for multi-device setups.
# =============================================================================
_target_: fusion_bench.method.SimpleEnsembleAlgorithm
device_map: null # Set to null for single device, or specify mapping

create a simple ensemble of CLIP-ViT models for image classification tasks.

fusion_bench \
  method=ensemble/simple_ensemble \
  modelpool=CLIPVisionModelPool/clip-vit-base-patch32_TA8 \
  taskpool=CLIPVisionModelTaskPool/clip-vit-classification_TA8

API Usage

The following Python code snippet demonstrates how to use the SimpleEnsembleAlgorithm class from the fusion_bench.method module to create a simple ensemble of PyTorch models.

from fusion_bench.method import SimpleEnsembleAlgorithm

# Instantiate the SimpleEnsembleAlgorithm
algorithm = SimpleEnsembleAlgorithm()

# Assume we have a list of PyTorch models (nn.Module instances) or a modelpool that we want to ensemble.
models = [...]

# Run the algorithm on the modelpool or models.
ensemble_model = algorithm.run(modelpool)  # or algorithm.run(models)

Here's a step-by-step explanation:

  1. Instantiate the SimpleEnsembleAlgorithm:

    • The algorithm requires no parameters for initialization since it uses equal weights for all models.

  2. Prepare your models:

    • You can either use a BaseModelPool instance that contains your models, or directly provide a list of PyTorch nn.Module instances.
    • The algorithm will load models from the modelpool using modelpool.load_model() for each model name.

  3. Run the algorithm:

    • The run method processes the modelpool and returns an EnsembleModule that represents the simple ensemble of the input models.
    • The resulting ensemble computes the average of all model predictions.

Implementation Details