Requirements

Before you can run the example, you need to configure a cluster and upload data to the cloud. In MATLAB, you can create clusters in the cloud directly from the MATLAB Desktop. On the Home tab, in the Parallel menu, select Create and Manage Clusters. In the Cluster Profile Manager, click Create Cloud Cluster. Alternatively, you can use MathWorks Cloud Center to create and access compute clusters. For more information, see Getting Started with Cloud Center. After that, upload your data to an Amazon S3 bucket and access it directly from MATLAB. This example uses a copy of the CIFAR-10 data set that is already stored in Amazon S3. For instructions, see Upload Deep Learning Data to the Cloud (Deep Learning Toolbox).

Set Up Parallel Pool

Start a parallel pool in the cluster and set the number of workers to the number of GPUs in your cluster. If you specify more workers than GPUs, then the remaining workers are idle. This example assumes that the cluster you are using is set as the default cluster profile. Check the default cluster profile on the MATLAB Home tab, in Parallel > Select a Default Cluster.

numberOfWorkers = 8;
parpool(numberOfWorkers);

Starting parallel pool (parpool) using the 'MyClusterInTheCloud' profile ...
connected to 8 workers.

Load Data Set from the Cloud

Load the training and test data sets from the cloud using imageDatastore. In this example, you use a copy of the CIFAR-10 data set stored in Amazon S3. To ensure that the workers have access to the datastore in the cloud, make sure that the environment variables for the AWS credentials are set correctly. See Upload Deep Learning Data to the Cloud (Deep Learning Toolbox).

imdsTrain = imageDatastore('s3://cifar10cloud/cifar10/train', ...
 'IncludeSubfolders',true, ...
 'LabelSource','foldernames');

imdsTest = imageDatastore('s3://cifar10cloud/cifar10/test', ...
 'IncludeSubfolders',true, ...
 'LabelSource','foldernames');

Train the network with augmented image data by creating an augmentedImageDatastore object. Use random translations and horizontal reflections. Data augmentation helps prevent the network from overfitting and memorizing the exact details of the training images.

imageSize = [32 32 3];
pixelRange = [-4 4];
imageAugmenter = imageDataAugmenter( ...
    'RandXReflection',true, ...
    'RandXTranslation',pixelRange, ...
    'RandYTranslation',pixelRange);
augmentedImdsTrain = augmentedImageDatastore(imageSize,imdsTrain, ...
    'DataAugmentation',imageAugmenter, ...
    'OutputSizeMode','randcrop');

Define Network Architecture and Training Options

Define a network architecture for the CIFAR-10 data set. To simplify the code, use convolutional blocks that convolve the input. The pooling layers downsample the spatial dimensions.

blockDepth = 4; % blockDepth controls the depth of a convolutional block
netWidth = 32; % netWidth controls the number of filters in a convolutional block

layers = [
    imageInputLayer(imageSize) 
    
    convolutionalBlock(netWidth,blockDepth)
    maxPooling2dLayer(2,'Stride',2)
    convolutionalBlock(2*netWidth,blockDepth)
    maxPooling2dLayer(2,'Stride',2)    
    convolutionalBlock(4*netWidth,blockDepth)
    averagePooling2dLayer(8) 
    
    fullyConnectedLayer(10)
    softmaxLayer
    classificationLayer
];

Define the training options. Train the network in parallel using the current cluster, by setting the execution environment to parallel. When you use multiple GPUs, you increase the available computational resources. Scale up the mini-batch size with the number of GPUs to keep the workload on each GPU constant. Scale the learning rate according to the mini-batch size. Use a learning rate schedule to drop the learning rate as the training progresses. Turn on the training progress plot to obtain visual feedback during training.

miniBatchSize = 256 * numberOfWorkers;
initialLearnRate = 1e-1 * miniBatchSize/256;

options = trainingOptions('sgdm', ...
    'ExecutionEnvironment','parallel', ... % Turn on automatic parallel support.
    'InitialLearnRate',initialLearnRate, ... % Set the initial learning rate.
    'MiniBatchSize',miniBatchSize, ... % Set the MiniBatchSize.
    'Verbose',false, ... % Do not send command line output.
    'Plots','training-progress', ... % Turn on the training progress plot.
    'L2Regularization',1e-10, ...
    'MaxEpochs',50, ...
    'Shuffle','every-epoch', ...
    'ValidationData',imdsTest, ...
    'ValidationFrequency',floor(numel(imdsTrain.Files)/miniBatchSize), ...
    'LearnRateSchedule','piecewise', ...
    'LearnRateDropFactor',0.1, ...
    'LearnRateDropPeriod',45);

Train Network and Use for Classification

Train the network in the cluster. During training, the plot displays the progress.

net = trainNetwork(augmentedImdsTrain,layers,options)

net = 
  SeriesNetwork with properties:

    Layers: [43×1 nnet.cnn.layer.Layer]

Determine the accuracy of the network, by using the trained network to classify the test images on your local machine. Then compare the predicted labels to the actual labels.

YPredicted = classify(net,imdsTest);
accuracy = sum(YPredicted == imdsTest.Labels)/numel(imdsTest.Labels)

Define Helper Function

Define a function to create a convolutional block in the network architecture.

function layers = convolutionalBlock(numFilters,numConvLayers)
    layers = [
        convolution2dLayer(3,numFilters,'Padding','same')
        batchNormalizationLayer
        reluLayer
    ];
    
    layers = repmat(layers,numConvLayers,1);
end