Snapshot Ensembles

This repository contains an implementation in Keras of the paper Snapshot Ensembles: Train 1, get M for free.

The authors use a modified version of cyclical learning rate to force the model to fall into local minima at the end of each cycle. Each local minima makes different mistakes. Thus the ensemble of every local minima helps to reach a better generalization.

Prototype

This is a callback:

Snapshot(folder_path, nb_epochs, nb_cycles=5, verbose=0)

With:

• folder_path: The folder path where every cycle weights will be stored. If the folder does not exist, it will be created.
• nb_epochs: The total number of epoch. Necessary to compute the learning rate modifier formula.
• nb_cycles: The number of cycles, must be inferior to the number of epochs.
• verbose: If verbose is greater than 0, messages will be printed when the learning rate is modified or a cycle has been saved.

Usage

from snapshot import Snapshot

callback = Snapshot('snapshots', nb_epochs=6, verbose=1, nb_cycles=2)
model.fit(
    x=x_train, y=y_train,
    epochs=10,
    batch_size=32,
    callbacks=[callback]
)

The authors advise to use the mean of the models'outputs. The file example.py shows how one could do it.