Daniel Voigt Godoy - Deep Learning with PyTorch Step-by-Step A Beginner’s Guide-leanpub

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What’s Next?It’s time to set up an environment for your learning journey using the Setup Guide.[3] https://bit.ly/2MQoYRo[4] https://bit.ly/37uZgLB[5] https://pytorch.org/ecosystem/[6] https://bit.ly/2MTN0Lh[7] https://bit.ly/2UFHFve[8] https://bit.ly/2XXJkyo[9] https://openai.com/blog/openai-pytorch/[10] https://docs.fast.ai/[11] https://course.fast.ai/[12] https://course.fast.ai/[13] http://pyro.ai/[14] https://github.com/horovod/horovod[15] https://bit.ly/30CPhm5[16] https://bit.ly/3cT1aH2What’s Next? | 7
Setup GuideOfficial RepositoryThis book’s official repository is available on GitHub:https://github.com/dvgodoy/PyTorchStepByStepIt contains one Jupyter notebook for every chapter in this book. Each notebookcontains all the code shown in its corresponding chapter, and you should be able torun its cells in sequence to get the same outputs, as shown in the book. I stronglybelieve that being able to reproduce the results brings confidence to the reader.Even though I did my best to ensure the reproducibility of theresults, you may still find some minor differences in your outputs(especially during model training). Unfortunately, completelyreproducible results are not guaranteed across PyTorch releases,and results may not be reproducible between CPU and GPUexecutions, even when using identical seeds. [17]EnvironmentThere are three options for you to run the Jupyter notebooks:• Google Colab (https://colab.research.google.com)• Binder (https://mybinder.org)• Local InstallationLet’s briefly explore the pros and cons of each of these options.Google ColabGoogle Colab "allows you to write and execute Python in your browser, with zeroconfiguration required, free access to GPUs and easy sharing." [18] .You can easily load notebooks directly from GitHub using Colab’s special URL(https://colab.research.google.com/github/). Just type in the GitHub’s user ororganization (like mine, dvgodoy), and it will show you a list of all its publicrepositories (like this book’s, PyTorchStepByStep).8 | Setup Guide
Page 2 and 3: Deep Learning with PyTorchStep-by-S
Page 4 and 5: "What I cannot create, I do not und
Page 6 and 7: Train-Validation-Test Split. . . .
Page 8 and 9: Random Split. . . . . . . . . . . .
Page 10 and 11: The Precision Quirk . . . . . . . .
Page 12 and 13: A REAL Filter . . . . . . . . . . .
Page 14 and 15: Jupyter Notebook . . . . . . . . .
Page 16 and 17: Stacked RNN . . . . . . . . . . . .
Page 18 and 19: Attention Mechanism . . . . . . . .
Page 20 and 21: 4. Positional Encoding. . . . . . .
Page 22 and 23: Model Configuration & Training . .
Page 24 and 25: AcknowledgementsFirst and foremost,
Page 26 and 27: Frequently Asked Questions (FAQ)Why
Page 28 and 29: There is yet another advantage of f
Page 30 and 31: • Classes and methods are written
Page 34 and 35: After choosing a repository, it wil
Page 36 and 37: 1. AnacondaIf you don’t have Anac
Page 38 and 39: 3. PyTorchPyTorch is the coolest de
Page 40 and 41: (pytorchbook) C:\> conda install py
Page 42 and 43: (pytorchbook)$ pip install torchviz
Page 44 and 45: 7. JupyterAfter cloning the reposit
Page 46 and 47: Part IFundamentals| 21
Page 48 and 49: notebook. If not, just click on Cha
Page 50 and 51: Also, let’s say that, on average,
Page 52 and 53: There is one exception to the "alwa
Page 54 and 55: Random Initialization1 # Step 0 - I
Page 56 and 57: Batch, Mini-batch, and Stochastic G
Page 58 and 59: Outputarray([[-2. , -1.94, -1.88, .
Page 60 and 61: one matrix for each data point, eac
Page 62 and 63: Sure, different values of b produce
Page 64 and 65: Output-3.044811379650508 -1.8337537
Page 66 and 67: each parameter using the chain rule
Page 68 and 69: What’s the impact of one update o
Page 70 and 71: gradients, we know we need to take
Page 72 and 73: Very High Learning RateWait, it may
Page 74 and 75: true_b = 1true_w = 2N = 100# Data G
Page 76 and 77: Let’s look at the cross-sections
Page 78 and 79: Zero Mean and Unit Standard Deviati
Page 80 and 81: Sure, in the real world, you’ll n
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computing the loss, as shown in the
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• visualizing the effects of usin
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If you’re using Jupyter’s defau
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Notebook Cell 1.1 - Splitting synth
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Step 2# Step 2 - Computing the loss
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Output[0.49671415] [-0.1382643][0.8
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Notebook Cell 1.2 - Implementing gr
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# Sanity Check: do we get the same
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Outputtensor(3.1416)tensor([1, 2, 3
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Outputtensor([[1., 2., 1.],[1., 1.,
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dummy_array = np.array([1, 2, 3])du
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n_cudas = torch.cuda.device_count()
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back_to_numpy = x_train_tensor.nump
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I am assuming you’d like to use y
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Outputtensor([0.1940], device='cuda
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print(error.requires_grad, yhat.req
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Output(tensor([0.], device='cuda:0'
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56 # need to tell it to let it go..
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computation.If you chose "Local Ins
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Figure 1.6 - Now parameter "b" does
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There are many optimizers: SGD is t
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41 optimizer.zero_grad() 34243 prin
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Notebook Cell 1.8 - PyTorch’s los
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Outputarray(0.00804466, dtype=float
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Let’s build a proper (yet simple)
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"What do we need this for?"It turns
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1 Instantiating a model2 What IS th
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In the __init__() method, we create
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LayersA Linear model can be seen as
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There are MANY different layers tha
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We use magic, just like that:%run -
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• Step 1: compute model’s predi
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RecapFirst of all, congratulations
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Chapter 2Rethinking the Training Lo
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Let’s take a look at the code onc
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Higher-Order FunctionsAlthough this
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def exponentiation_builder(exponent
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Apart from returning the loss value
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Our code should look like this; see
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There is no need to load the whole
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but if we want to get serious about
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How does this change our code so fa
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Run - Model Training V2%run -i mode
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piece of code that’s going to be
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for it. We could do the same for th
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EvaluationHow can we evaluate the m
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And then, we update our model confi
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Run - Model Training V4%run -i mode
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Loading Extension# Load the TensorB
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browser, you’ll likely see someth
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model’s graph (not quite the same
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Figure 2.5 - Scalars on TensorBoard
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Define - Model Training V51 %%write
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If, by any chance, you ended up wit
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The procedure is exactly the same,
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soon, so please bear with me for no
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After recovering our model’s stat
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Run - Model Configuration V31 # %lo
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This is the general structure you
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Chapter 2.1Going ClassySpoilersIn t
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# A completely empty (and useless)
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# These attributes are defined here
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# Creates the train_step function f
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# Builds function that performs a s
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setattrThe setattr function sets th
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See? We effectively modified the un
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the random seed as arguments.This s
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The current state of development of
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Lossesdef plot_losses(self):fig = p
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Run - Data Preparation V21 # %load
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Model TrainingWe start by instantia
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Making PredictionsLet’s make up s
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OutputOrderedDict([('0.weight', ten
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Run - Data Preparation V21 # %load
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• defining our StepByStep class
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import numpy as npimport torchimpor
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Next, we’ll standardize the featu
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Equation 3.1 - A linear regression
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The odds ratio is given by the rati
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As expected, probabilities that add
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Sigmoid Functiondef sigmoid(z):retu
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A picture is worth a thousand words
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OutputOrderedDict([('linear.weight'
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The first summation adds up the err
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IMPORTANT: Make sure to pass the pr
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To make it clear: In this chapter,
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argument of nn.BCEWithLogitsLoss().
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It is not that hard, to be honest.
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Figure 3.6 - Training and validatio
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Outputarray([[0.5504593 ],[0.949995
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decision boundary.Look at the expre
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Are my data points separable?That
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model = nn.Sequential()model.add_mo
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It looks like this:Figure 3.10 - Sp
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True and False Positives and Negati
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tpr_fpr(cm_thresh50)Output(0.909090
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The trade-off between precision and
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Figure 3.13 - Using a low threshold
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Figure 3.16 - Trade-offs for two di
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thresholds do not necessarily inclu
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actual data, it is as bad as it can
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If you want to learn more about bot
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Model Training1 n_epochs = 10023 sb
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step in your journey! What’s next
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Chapter 4Classifying ImagesSpoilers
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Data GenerationOur images are quite
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Images and ChannelsIn case you’re
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image_rgb = np.stack([image_r, imag
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That’s fairly straightforward; we
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• Transformations based on Tensor
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position of an object in a picture
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Outputtensor([[[0., 0., 0., 1., 0.]
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Outputtensor([[[-1., -1., -1., 1.,
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We can convert the former into the
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composer = Compose([RandomHorizonta
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Output<torch.utils.data.dataset.Sub
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train_composer = Compose([RandomHor
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The minority class should have the
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train_loader = DataLoader(dataset=t
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implemented in Chapter 2.1? Let’s
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Let’s take one mini-batch of imag
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What does our model look like? Visu
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Model TrainingLet’s train our mod
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preceding hidden layer to compute i
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fig = sbs_nn.plot_losses()Figure 4.
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Equation 4.2 - Equivalence of deep
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w_nn_equiv = w_nn_output.mm(w_nn_hi
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Weights as PixelsDuring data prepar
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is only 0.25 (for z = 0) and that i
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nn.Tanh()(dummy_z)Outputtensor([-0.
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dummy_z = torch.tensor([-3., 0., 3.
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As you can see, in PyTorch the coef
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Figure 4.16 - Deep model (for real)
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Figure 4.18 - Losses (before and af
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Equation 4.3 - Activation functions
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Helper Function #41 def index_split
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Model Configuration1 # Sets learnin
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Bonus ChapterFeature SpaceThis chap
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Affine TransformationsAn affine tra
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Figure B.3 - Annotated model diagra
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Figure B.5 - In the beginning…But
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OK, now we can clearly see a differ
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In the model above, the sigmoid fun
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the more dimensions, the more separ
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import randomimport numpy as npfrom
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identity = np.array([[[[0, 0, 0],[0
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Figure 5.4 - Striding the image, on
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Output-----------------------------
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Outputtensor([[[[9., 5., 0., 7.],[0
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OutputParameter containing:tensor([
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Moreover, notice that if we were to
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In code, as usual, PyTorch gives us
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Outputtensor([[[[5., 5., 0., 8., 7.
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edge = np.array([[[[0, 1, 0],[1, -4
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A pooling kernel of two-by-two resu
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Outputtensor([[22., 23., 11., 24.,
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Figure 5.15 - LeNet-5 architectureS
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• second block: produces 16-chann
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Transformed Dataset1 class Transfor
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LossNew problem, new loss. Since we
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Outputtensor([4.0000, 1.0000, 0.500
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The loss only considers the predict
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Outputtensor([[-1.5229, -0.3146, -2
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IMPORTANT: I can’t stress this en
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figures at the beginning of this ch
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The three units in the output layer
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StepByStep Method@staticmethoddef _
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The meow() method is totally indepe
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StepByStep Methoddef visualize_filt
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dummy_model = nn.Linear(1, 1)dummy_
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dummy_listOutput[(Linear(in_feature
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Output{Conv2d(1, 1, kernel_size=(3,
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will be the externally defined vari
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Removing Hookssbs_cnn1.remove_hooks
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return figsetattr(StepByStep, 'visu
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Figure 5.22 - Feature maps (classif
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classification: The predicted class
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convolutional layers to our model a
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Capturing Outputsfeaturizer_layers
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the filters learned by the model pr
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given chapter are imported at its v
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Data PreparationThe data preparatio
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model anyway. We’ll use it to com
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StepByStep Method@staticmethoddef m
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"What’s wrong with the colors?"Th
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three_channel_filter = np.array([[[
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Fancier Model (Constructor)class CN
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Fancier Model (Classifier)def class
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torch.manual_seed(44)dropping_model
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Outputtensor([0.1000, 0.2000, 0.300
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Figure 6.8 - Output distribution fo
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Adaptive moment estimation (Adam) u
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torch.manual_seed(13)# Model Config
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Outputtorch.Size([5, 3, 3, 3])Its s
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Choosing a learning rate that works
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Higher-Order Learning Rate Function
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Perfect! Now let’s build the actu
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ax.set_xlabel('Learning Rate')ax.se
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LRFinderThe function we’ve implem
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value in our moving average has an
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Figure 6.15 - Distribution of weigh
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In code, the implementation of the
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As expected, the EWMA without corre
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optimizer = optim.Adam(model.parame
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IMPORTANT: The logging function mus
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Output{'state': {140601337662512: {
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different optimizer, set them to ca
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• dampening: dampening factor for
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Figure 6.20 - Paths taken by SGD (w
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Equation 6.16 - Looking aheadOnce N
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Figure 6.22 - Path taken by each SG
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for epoch in range(4):# training lo
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course) up to a given number of epo
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Next, we create a protected method
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Mini-Batch SchedulersThese schedule
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Schedulers in StepByStep — Part I
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Scheduler PathsBefore trying out a
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After applying each scheduler to SG
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Data Preparation1 # Loads temporary
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Figure 6.31 - LossesEvaluationprint
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[96] http://www.samkass.com/theorie
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ImportsFor the sake of organization
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ILSVRC-2012The 2012 edition [111] o
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remained unchanged.ResNet (MSRA Tea
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Transfer Learning in PracticeIn Cha
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dropout. You’re already familiar
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OutputDownloading: "https://downloa
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Replacing the "Top" of the Model1 a
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Model Size Classifier Layer(s) Repl
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Model TrainingWe have everything se
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"Removing" the Top Layer1 alex.clas
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torch.save(train_preproc.tensors, '
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Outputtensor([[109, 124],[124, 124]
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Model Configuration1 optimizer_mode
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Figure 7.4 - 1x1 convolutionThe inp
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The weights used by PIL are 0.299 f
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• reduce the number of output cha
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The constructor method defines the
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Does it sound familiar? That’s wh
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and w to represent these parameters
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A mini-batch of size 64 is small en
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normed1 = batch_normalizer(batch1[0
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OutputOrderedDict([('running_mean',
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OutputOrderedDict([('running_mean',
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batch_normalizer = nn.BatchNorm2d(n
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torch.manual_seed(23)dummy_points =
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np.concatenate([dummy_points[:5].nu
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Another advantage of these shortcut
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It should be pretty clear, except f
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Data Preparation1 # ImageNet statis
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Data Preparation — Preprocessing1
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• freezing the layers of the mode
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Extra ChapterVanishing and Explodin
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discussing it, let me illustrate it
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Model Configuration (2)1 loss_fn =
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weights. If done properly, the init
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just did), or, if you are training
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Figure E.3 - The effect of batch no
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Model Configuration1 torch.manual_s
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torch.manual_seed(42)parm = nn.Para
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(and only if) the norm exceeds the
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if callable(self.clipping): 1self.c
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Moreover, let’s use a ten times h
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Clipping with HooksFirst, we reset
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• visualizing the difference betw
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Chapter 8SequencesSpoilersIn this c
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Before shuffling, the pixels were o
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And then let’s visualize the firs
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sequence so far, and a data point f
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Considering this, the not "unrolled
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linear_input = nn.Linear(n_features
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Outputtensor([[0.3924, 0.8146]], gr
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Now we’re talking! The last hidde
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Let’s take a look at the RNN’s
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◦ The initial hidden state, which
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batch_first argument to True so we
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OutputOrderedDict([('weight_ih_l0',
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out, hidden = rnn_stacked(x)out, hi
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_l0_reverse).Once again, let’s cr
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For bidirectional RNNs, the last el
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Model Configuration1 class SquareMo
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StepByStep.loader_apply(test_loader
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Figure 8.14 - Final hidden states f
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Figure 8.16 - Transforming the hidd
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Since the RNN cell has both of them
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Every gate worthy of its name will
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• For r=0 and z=0, the cell becom
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In code, we can use split() to get
Page 658 and 659:
Let’s pause for a moment here. Fi
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Square Model II — The QuickeningT
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Outputtensor([[53, 53],[75, 75]])Th
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Figure 8.22 - Transforming the hidd
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Equation 8.9 - LSTM—candidate hid
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Now, let’s visualize the internal
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OutputOrderedDict([('weight_ih', te
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def forget_gate(h, x):thf = f_hidde
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Outputtensor([[-5.4936e-02, -8.3816
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1 First change: from RNN to LSTM2 S
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Like the GRU, the LSTM presents fou
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Output-----------------------------
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Before moving on to packed sequence
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column-wise fashion, from top to bo
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does match the last output.• No,
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So, to actually get the last output
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Data Preparation1 class CustomDatas
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OutputPackedSequence(data=tensor([[
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Model Configuration & TrainingWe ca
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size = 5weight = torch.ones(size) *
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torch.manual_seed(17)conv_seq = nn.
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Figure 8.32 - Applying dilated filt
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Model Configuration1 torch.manual_s
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We can actually find an expression
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Data Preparation1 def pack_collate(
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and variable-length sequences.Model
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• generating variable-length sequ
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import copyimport numpy as npimport
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Figure 9.3 - Sequence datasetThe co
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coordinates of a "perfect" square a
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Let’s pretend for a moment that t
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to initialize the hidden state and
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predictions in previous steps have
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the second set of predicted coordin
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Let’s create an instance of the m
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Model Configuration & TrainingThe m
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Sure, we can!AttentionHere is a (no
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based on "the" and "zone," I’ve j
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Figure 9.12 - Matching a query to t
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Outputtensor([[[ 0.0832, -0.0356],[
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utmost importance for the correct i
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Its formula is:Equation 9.3 - Cosin
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second hidden state contributes to
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Outputtensor([[[ 0.5475, 0.0875, -1
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alphas = F.softmax(scaled_products,
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Outputtensor([[[ 0.2138, -0.3175]]]
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Attention Mechanism1 class Attentio
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"Why would I want to force it to do
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1 Sets attention module and adjusts
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encdec = EncoderDecoder(encoder, de
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fig = sbs_seq_attn.plot_losses()Fig
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Figure 9.20 - Attention scoresSee?
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Wide vs Narrow AttentionThis mechan
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"What’s so special about it?"Even
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Once again, the affine transformati
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Next, we shift our focus to the sel
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Encoder + Self-Attention1 class Enc
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Figure 9.27 - Encoder with self- an
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The figure below depicts the self-a
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shifted_seq = torch.cat([source_seq
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Equation 9.17 - Decoder’s (masked
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At evaluation / prediction time we
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Outputtensor([[[0.4132, 0.3728],[0.
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Figure 9.33 - Encoder + decoder + a
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64 return outputsThe encoder-decode
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Figure 9.34 - Losses—encoder + de
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curse. On the one hand, it makes co
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"Are we done now? Is this good enou
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Figure 9.46 - Consistent distancesA
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Let’s recap what we’ve already
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Let’s see it in code:max_len = 10
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Let’s put it all together into a
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Outputtensor([[[-1.0000, 0.0000],[-
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Decoder with Positional Encoding1 c
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Visualizing PredictionsLet’s plot
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Next, we’re moving on to the thre
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Data Generation & Preparation1 # Tr
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59 self.trg_masks)60 else:61 # Deco
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Model Configuration1 class EncoderS
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1617 @property18 def alphas(self):1
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Output(0.016193246061448008, 0.0341
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sequential order of the data• fig
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following imports:import copyimport
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Figure 10.2 - Chunking: the wrong a
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chunks to compute the other half of
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67 # N, L, n_heads, d_k68 context =
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dummy_points = torch.randn(16, 2, 4
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Stacking Encoders and DecodersLet
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"… with great depth comes great c
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Transformer EncoderWe’ll be repre
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Let’s see it in code, starting wi
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Transformer Encoder1 class EncoderT
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of the encoder-decoder (or Transfor
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In PyTorch, the decoder "layer" is
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In PyTorch, the decoder is implemen
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Equation 10.7 - Data points' means
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layer_norm = nn.LayerNorm(d_model)n
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Figure 10.10 - Layer norm vs batch
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Outputtensor([[[ 1.4636, 2.3663],[
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The TransformerLet’s start with t
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"values") in the decoder.• decode
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Data Preparation1 # Generating trai
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Figure 10.15 - Losses—Transformer
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• First, and most important, PyTo
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decode(), with a single one, encode
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46 for i in range(self.target_len):
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Figure 10.18 - Losses - PyTorch’s
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Figure 10.20 - Sample image—label
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4041 # Builds a weighted random sam
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Figure 10.23 - Sample image—split
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Einops"There is more than one way t
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Figure 10.26 - Two patch embeddings
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Now each sequence has ten elements,
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It takes an instance of a Transform
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Putting It All TogetherIn this chap
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1. Encoder-DecoderThe encoder-decod
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This is the actual encoder-decoder
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3. DecoderThe Transformer decoder h
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5. Encoder "Layer"The encoder "laye
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7. "Sub-Layer" WrapperThe "sub-laye
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8. Multi-Headed AttentionThe multi-
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Model Configuration & TrainingModel
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• training the Transformer to tac
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Part IVNatural Language Processing|
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Additional SetupThis is a special c
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"Down the Yellow Brick Rabbit Hole"
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The actual texts of the books are c
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"What is this punkt?"That’s the P
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14 # If there is a configuration fi
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Sentence Tokenization in spaCyBy th
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AttributesThe Dataset has many attr
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Output{'labels': 1,'sentence': 'The
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elements from the text. But preproc
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Data AugmentationLet’s briefly ad
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The corpora’s dictionary is not a
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Finally, if we want to convert a li
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Once we’re happy with the size an
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from transformers import BertTokeni
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"What about the separation token?"T
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The last output, attention_mask, wo
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Outputtensor([[ 3, 27, 1, ..., 0, 0
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vector, right? And our vocabulary i
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Maybe you filled this blank in with
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Continuous Bag-of-Words (CBoW)In th
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That’s a fairly simple model, rig
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Figure 11.13 - Continuous bag-of-wo
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Figure 11.15 - Reviewing restaurant
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You got that right—arithmetic—r
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There we go, 50 dimensions! It’s
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Equation 11.1 - Embedding arithmeti
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Only 82 out of 50,802 words in the
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Now we can use its encode() method
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Model I — GloVE + ClassifierData
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Pre-trained PyTorch EmbeddingsThe e
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Model Configuration & TrainingLet
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6 self.encoder = encoder7 self.mlp
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Figure 11.20 - Losses—Transformer
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Outputtensor([[[2.6334e-01, 6.9912e
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I want to introduce you to…ELMoBo
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OutputToken: 32 watchThe get_token(
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Helper Function to Retrieve Embeddi
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Output(tensor(-0.5047, device='cuda
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torch.all(new_flair_sentences[0].to
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Outputtensor(0.3504, device='cuda:0
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We can leverage this fact to slight
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We can easily get the embeddings fo
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Figure 11.24 - Losses—simple clas
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We can inspect the pre-trained mode
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Every word piece is prefixed with #
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far, our models used these embeddin
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position_ids = torch.arange(512).ex
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Pre-training TasksMasked Language M
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Then, let’s create an instance of
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If these two sentences were the inp
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The BERT model may take many other
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The contextual word embeddings are
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Model Configuration1 class BERTClas
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"Which BERT is that? DistilBERT?!"D
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Well, you probably don’t want to
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set num_labels=1 as argument.If you
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Output{'attention_mask': [1, 1, 1,
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OutputTrainingArguments(output_dir=
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Method for Computing Accuracy1 def
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loaded_model = (AutoModelForSequenc
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logits.logits.argmax(dim=1)Outputte
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For a complete list of available ta
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[215]. For a demo of GPT-2’s capa
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in Chapter 9, and I reproduce it be
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Data Preparation1 auto_tokenizer =
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Data Preparation1 lm_train_dataset
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The training arguments are roughly
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device_index = (model.device.indexi
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• learning that a language model
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[167] https://huggingface.co/docs/d
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