This repository contains the code for the paper Snapshot Ensemble: Train 1, Get M for Free.

The code is based on fb.resnet.torch by Facebook (https://github.com/facebook/fb.resnet.torch).

##Table of Contents 0. Introduction 0. Usage 0. Contact

##Introduction Snapshot Ensemble is a method to obtain ensembles of multiple neural network at no additional training cost. This is achieved by letting a single neural network converge into several local minima along its optimization path and save the model parameters. The repeated rapid convergence is realized using multiple learning rate annealing cycles.

Figure 1: Left: Illustration of SGD optimization with a typical learning rate schedule. The model converges to a minimum at the end of training. Right: Illustration of Snapshot Ensembling optimization. The model undergoes several learning rate annealing cycles, converging to and escaping from multiple local minima. We take a snapshot at each minimum for test time ensembling.

##Usage 0. Install Torch ResNet (https://github.com/facebook/fb.resnet.torch);

1. Replace train.lua with the one from this repository;

2. Add the follwoing options to opts.lua to support learning rate with cosine annealing

cmd:option('-lrShape', 'multistep', 'learning rate annealing function, multistep or cosine') cmd:option('-nCycles', '1', 'number of learning rate annealing cycles')

3. An example command to train a Snapshot Ensemble with ResNet-110 (B = 200 epochs, M = 5 cycles, Initial learning rate alpha = 0.1) on CIFAR-100:

th main.lua -netType resnet -depth 110 -dataset cifar100 -batchSize 64 -nEpochs 200 -lrShape cosine -nCycles 5 -LR 0.1 -save checkpoints/

##Contact gh349 at cornell.edu
Any discussions, suggestions and questions are welcome!