Digit Classification

Use the MNIST database of handwritten digits to train a convolutional network to predict the digit given an image.

First obtain the training and validation data.

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resource = ResourceObject["MNIST"]; trainingData = ResourceData[resource, "TrainingData"]; testData = ResourceData[resource, "TestData"];

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RandomSample[trainingData, 5]

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Define a convolutional neural network that takes in 28×28 grayscale images as input.

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lenet = NetChain[ {ConvolutionLayer[20, 5], Ramp, PoolingLayer[2, 2], ConvolutionLayer[50, 5], Ramp, PoolingLayer[2, 2], FlattenLayer[], 500, Ramp, 10, SoftmaxLayer[]}, "Output" -> NetDecoder[{"Class", Range[0, 9]}], "Input" -> NetEncoder[{"Image", {28, 28}, "Grayscale"}] ]

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Train the network for four training rounds.

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lenet = NetTrain[lenet, trainingData, ValidationSet -> testData, MaxTrainingRounds -> 3];

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Evaluate the trained network directly on images randomly sampled from the validation set.

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imgs = Keys @ RandomSample[testData, 5]; Thread[imgs -> lenet[imgs]]

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