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Dhairya Gandhi fixes 935a990 Oct 1, 2019
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@staticfloat @MikeInnes @dhairyagandhi96 @SudhanshuAgrawal27 @sambitdash @fps
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# Classifies MNIST digits with a convolutional network.
# Writes out saved model to the file "mnist_conv.bson".
# Demonstrates basic model construction, training, saving,
# conditional early-exit, and learning rate scheduling.
#
# This model, while simple, should hit around 99% test
# accuracy after training for approximately 20 epochs.
using Flux, Flux.Data.MNIST, Statistics
using Flux: onehotbatch, onecold, crossentropy, throttle
using Base.Iterators: repeated, partition
using Printf, BSON
# Load labels and images from Flux.Data.MNIST
@info("Loading data set")
train_labels = MNIST.labels()
train_imgs = MNIST.images()
# Bundle images together with labels and group into minibatchess
function make_minibatch(X, Y, idxs)
X_batch = Array{Float32}(undef, size(X[1])..., 1, length(idxs))
for i in 1:length(idxs)
X_batch[:, :, :, i] = Float32.(X[idxs[i]])
end
Y_batch = onehotbatch(Y[idxs], 0:9)
return (X_batch, Y_batch)
end
batch_size = 128
mb_idxs = partition(1:length(train_imgs), batch_size)
train_set = [make_minibatch(train_imgs, train_labels, i) for i in mb_idxs]
# Prepare test set as one giant minibatch:
test_imgs = MNIST.images(:test)
test_labels = MNIST.labels(:test)
test_set = make_minibatch(test_imgs, test_labels, 1:length(test_imgs))
# Define our model. We will use a simple convolutional architecture with
# three iterations of Conv -> ReLU -> MaxPool, followed by a final Dense
# layer that feeds into a softmax probability output.
@info("Constructing model...")
model = Chain(
# First convolution, operating upon a 28x28 image
Conv((3, 3), 1=>16, pad=(1,1), relu),
MaxPool((2,2)),
# Second convolution, operating upon a 14x14 image
Conv((3, 3), 16=>32, pad=(1,1), relu),
MaxPool((2,2)),
# Third convolution, operating upon a 7x7 image
Conv((3, 3), 32=>32, pad=(1,1), relu),
MaxPool((2,2)),
# Reshape 3d tensor into a 2d one, at this point it should be (3, 3, 32, N)
# which is where we get the 288 in the `Dense` layer below:
x -> reshape(x, :, size(x, 4)),
Dense(288, 10),
# Finally, softmax to get nice probabilities
softmax,
)
# Load model and datasets onto GPU, if enabled
train_set = gpu.(train_set)
test_set = gpu.(test_set)
model = gpu(model)
# Make sure our model is nicely precompiled before starting our training loop
model(train_set[1][1])
# `loss()` calculates the crossentropy loss between our prediction `y_hat`
# (calculated from `model(x)`) and the ground truth `y`. We augment the data
# a bit, adding gaussian random noise to our image to make it more robust.
function loss(x, y)
# We augment `x` a little bit here, adding in random noise
x_aug = x .+ 0.1f0*gpu(randn(eltype(x), size(x)))
y_hat = model(x_aug)
return crossentropy(y_hat, y)
end
accuracy(x, y) = mean(onecold(model(x)) .== onecold(y))
# Train our model with the given training set using the ADAM optimizer and
# printing out performance against the test set as we go.
opt = ADAM(0.001)
@info("Beginning training loop...")
best_acc = 0.0
last_improvement = 0
for epoch_idx in 1:100
global best_acc, last_improvement
# Train for a single epoch
Flux.train!(loss, params(model), train_set, opt)
# Calculate accuracy:
acc = accuracy(test_set...)
@info(@sprintf("[%d]: Test accuracy: %.4f", epoch_idx, acc))
# If our accuracy is good enough, quit out.
if acc >= 0.999
@info(" -> Early-exiting: We reached our target accuracy of 99.9%")
break
end
# If this is the best accuracy we've seen so far, save the model out
if acc >= best_acc
@info(" -> New best accuracy! Saving model out to mnist_conv.bson")
BSON.@save joinpath(dirname(@__FILE__), "mnist_conv.bson") model epoch_idx acc
best_acc = acc
last_improvement = epoch_idx
end
# If we haven't seen improvement in 5 epochs, drop our learning rate:
if epoch_idx - last_improvement >= 5 && opt.eta > 1e-6
opt.eta /= 10.0
@warn(" -> Haven't improved in a while, dropping learning rate to $(opt.eta)!")
# After dropping learning rate, give it a few epochs to improve
last_improvement = epoch_idx
end
if epoch_idx - last_improvement >= 10
@warn(" -> We're calling this converged.")
break
end
end
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