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DPS921/PyTorch: Convolutional Neural Networks

8,505 bytes added, 16:59, 30 November 2020
→‎Progress Report
3. Novell Rasam
 
== Progress ==
== Introduction to Neural Networks ==
Before we can dive into PyTorch, we need to introduce the general concepts behind Neural Networks and AI programing. You have probably heard of AI and machine learning, and have seen some examples of what they can do, but I wonder if you know the difference between AI, Machine Learning, and Deep Learning? The confusion usually comes from thinking of them as separate ideas, but it is more helpful to think of them as belonging to a hierarchy, where Machine Learning is a subset of AI, and Deep Learning is a smaller subset within the subset of Machine Learning. This handy infographic goes into more detail:
 [[File:Figure1.jpg]][https://medium.com/datadriveninvestor/infographics-digest-vol-3-da67e69d71ce] 
=== Machine Learning vs. Deep Learning ===
Even with the above infographic, there is still probably some confusion with what distinguishes Deep Learning from Machine Learning. If you are confused, it is an important reminder that everything it says about Machine Learning also applies to Deep Learning, “enable machines to improve with experience.” The main difference is that conventional Machine Learning algorithms require manual intervention in the area of feature extraction, while Deep Learning algorithms do it themselves. See the infographic below:
 [[File:Figure2.jpg]][https://www.analyticsvidhya.com/blog/2020/02/cnn-vs-rnn-vs-mlp-analyzing-3-types-of-neural-networks-in-deep-learning/] 
What this means is that Deep Learning algorithms have the added advantage that they can be setup randomly, with random weights and biases. And as along as we tell it what we want the output to be, let’s say a car, it will find out the best way to distinguish whether any given input is in indeed a car. In other words, it can teach itself. On the other hand, with traditional machine learning, the programmer would have to tell the algorithm what “features” to look for when determining if something was a car.
This type of neural network is probably the simplest and easiest to understand. The name Neural Network comes from the fact that their architecture is vaguely modelled off neurons in the brain. They can be activated like a neuron and they often linked with other neurons. The analogy is considered misleading, so I’ll stop it there. It’s better think of these artificial neurons as bits that can hold a value from zero to one, instead of only zero or one. For our purposes we want classify an image. So, the neural network starts by associating each pixel with a value, like previously mentioned, from zero to one. One represents a fully colored in pixel, while zero represents an empty pixel. See below:
 [[File:Figure3.png]][https://www.youtube.com/watch?v=aircAruvnKk] 
All these pixel neurons make up the first input layer. To get from a series of values to the final output decision, requires intervening layers. These “hidden” layers do a lot of the actual computation, and their job is to extract features from a given image of a number. These features are then used to determine if the image represents, for example, a nine.
 [[File:Figure4.png]][https://www.youtube.com/watch?v=aircAruvnKk] 
Each one of these hidden layer neurons, also called Perceptrons, is tasked with activating if it finds its corresponding feature. A programmer can initially set these features or set random features, but ultimately the ANN will come up with its own rules. It does this through constantly evolving weights and biases, which are stored in its Perceptrons. See the figure below:
 [[File:Figure5.gif]][https://www.analyticsvidhya.com/blog/2020/02/cnn-vs-rnn-vs-mlp-analyzing-3-types-of-neural-networks-in-deep-learning/] 
Composed of weights and a bias, a Perceptron gives each input a separate weight. It then takes the sum of all those values. In this case, the sum is w1x0.7 + w2x0.6 + w3x1.4. A bias is then added to the weighted sum to determine if the value is worthy enough for activation. The activation stage takes the result of the last step and squishes it into a number between zero and one. A value close to one suggests high activation; while zero suggests no activation. These activation values are often fed into a subsequent layer of Perceptrons.
Finally, the Perceptrons spit out confidence values for each possible number. For example, it might identity a number as a two with 90% confidence.
 [[File:Figure6.png]][https://www.youtube.com/watch?v=aircAruvnKk]
=== Back Propagation ===
As you might imagine, the ANN is unlikely to get it right the first time. In fact, it will undoubtedly get it wrong, horribly wrong! It improves itself by adjusting those weights and biases mentioned earlier. In order to do this, it must be trained with tons of example numbers, as well as a cheat sheet to check its answers. How far the ANN’s final answer is from the correct answer is called the cost. Once a cost is determined, the weights and biases that make up the ANN are adjusted to minimise this cost. That’s a lot of math I summed up in one sentence. The algorithm that does this math is called Back Propagation, and it’s how an ANN learns. It’s called that because it works backwards from what it wants the output to be, down the hidden layers. This is extremely computationally intensive because it usually has tens of thousands of answers to work backwards from.[https://www.youtube.com/watch?v=Ilg3gGewQ5U&list=PLZHQObOWTQDNU6R1_67000Dx_ZCJB-3pi&index=3]
What is commonly done instead is that the training data is split into batches and the back-prop algorithm is performed on each batch. This is not as accurate as performing it on the entire training set, but is good enough for the increase in performance. As you might imagine, each batch has an opportunity to be parallelized.
Convolutional Neural Networks are faster and more accurate at image recognition than standard ANNs. They achieve this by focusing on spatial features such as ears, nose, mouth, and by ignoring irrelevant data.
[[File:Figure7.gif]][https://www.analyticsvidhya.com/blog/2020/02/cnn-vs-rnn-vs-mlp-analyzing-3-types-of-neural-networks-in-deep-learning/]
== Implementation of a Neural Network ==
return t
== Data Parallelism ==  This section details a way to parallelize your NN .  As image recognition is graphical in nature, multiple GPUs are the best way to parallelize dataset training. <code>DataParallel</code> is a single-machine parallel model, that uses multiple GPUs [https://pytorch.org/tutorials/beginner/blitz/data_parallel_tutorial.html]. It is more convenient than a multi-machine, distributed training model. You can easily put your model on a GPU by writing:  device = torch.device("cuda:0") model.to(device) Then, you can copy all your tensors to the GPU:  mytensor = my_tensor.to(device) However, PyTorch will only use one GPU by default. In order to run on multiple GPUs you need to use <code>DataParallel</code>:  model = nn.DataParallel(model) ==== Imports and Parameters ==== Import the following modules and define your parameters:  import torch import torch.nn as nn from torch.utils.data import Dataset, DataLoader  # Parameters and DataLoaders input_size = 5 output_size = 2  batch_size = 30 data_size = 100 Device:  device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu") ==== Dummy DataSet ==== You can make a random dummy dataset:  class RandomDataset(Dataset):  def __init__(self, size, length): self.len = length self.data = torch.randn(length, size)  def __getitem__(self, index): return self.data[index]  def __len__(self): return self.len  rand_loader = DataLoader(dataset=RandomDataset(input_size, data_size), batch_size=batch_size, shuffle=True) ==== Simple Model ==== Here is a simple linear model definition, but <code>DataParallel</code> can be used any model (CNN, RNN, etc).  class Model(nn.Module): # Our model  def __init__(self, input_size, output_size): super(Model, self).__init__() self.fc = nn.Linear(input_size, output_size)  def forward(self, input): output = self.fc(input) print("\tIn Model: input size", input.size(), "output size", output.size())  return output ==== Create Model and DataParallel ==== Now that everything is defined, we need create an instance of the model and check if we have multiple GPUs.  model = Model(input_size, output_size) if torch.cuda.device_count() > 1: print("Let's use", torch.cuda.device_count(), "GPUs!") # dim = 0 [30, xxx] -> [10, ...], [10, ...], [10, ...] on 3 GPUs model = nn.DataParallel(model) # wrap model using nn.DataParallel  model.to(device) ==== Run the Model ==== The print statement will let us see the input and output sizes.  for data in rand_loader: input = data.to(device) output = model(input) print("Outside: input size", input.size(), "output_size", output.size()) ==== Results ==== If you have no GPU or only one GPU, the input and output size will match the batch size, so no parallelization. But if you have 2 GPUs, you'll get these results:  # on 2 GPUs Let's use 2 GPUs! In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2]) In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2]) Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2]) In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2]) In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2]) Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2]) In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2]) In Model: input size torch.Size([15, 5]) output size torch.Size([15, 2]) Outside: input size torch.Size([30, 5]) output_size torch.Size([30, 2]) In Model: input size torch.Size([5, 5]) output size torch.Size([5, 2]) In Model: input size torch.Size([5, 5]) output size torch.Size([5, 2]) Outside: input size torch.Size([10, 5]) output_size torch.Size([10, 2]) With 2 GPUs, the input and output sizes are half of 30, 15. === A More Intermediate Example === Here is a toy model that contains two linear layers. Each linear layer is designed to run a separate GPU [https://pytorch.org/tutorials/intermediate/model_parallel_tutorial.html].  import torch import torch.nn as nn import torch.optim as optim  class ToyModel(nn.Module): def __init__(self): super(ToyModel, self).__init__() self.net1 = torch.nn.Linear(10, 10).to('cuda:0') self.relu = torch.nn.ReLU() self.net2 = torch.nn.Linear(10, 5).to('cuda:1')  def forward(self, x): x = self.relu(self.net1(x.to('cuda:0'))) return self.net2(x.to('cuda:1')) The code is very similar to a single GPU implementation, except for the ''.to('cuda:x')'' calls, where ''cuda:0'' and ''cuda:1'' are each their own GPU [https://pytorch.org/tutorials/intermediate/model_parallel_tutorial.html].  model = ToyModel() loss_fn = nn.MSELoss() optimizer = optim.SGD(model.parameters(), lr=0.001)  optimizer.zero_grad() outputs = model(torch.randn(20, 10)) labels = torch.randn(20, 5).to('cuda:1') loss_fn(outputs, labels).backward() optimizer.step() The backward() and torch.optim will automatically take care of gradients as if the model is on one GPU. You only need to make sure that the labels are on the same device as the outputs when calling the loss function [https://pytorch.org/tutorials/intermediate/model_parallel_tutorial.html]. 
== Getting Started With Jupyter ==
pip install torch===1.7.0 torchvision===0.8.1 torchaudio===0.7.0 -f https://download.pytorch.org/whl/torch_stable.html
 
== Progress Report ==
 
*Update 1: Friday, November 27, 2020 - Started on Introduction to Neural Networks Section
*Update 2: Friday, November 27, 2020 - Installation and Configuration of Jupyter Lab
*Update 3: Saturday, November 28, 2020 - Practiced Working With and Learning About Jupyter Lab
*Update 4: Saturday, November 28, 2020 - Created a 4 layer ANN on Jupyter Lab
*Update 5: Saturday, November 28, 2020 - Initiated Training of the ANN and Verified Digit Recognition Capabilities
*Update 6: Sunday, November 29, 2020 - Finished Introduction to Neural Networks
*Update 7: Sunday, November 29, 2020 - Implemented a basic CNN Based on Previous Implementation of ANN
*Update 8: Monday, November 30, 2020 - Added Section on Data Parallel
 
==References==
*Khan, Faisa. “Infographics Digest - Vol. 3.” Medium, [https://medium.com/datadriveninvestor/infographics-digest-vol-3-da67e69d71ce]
*“ANN vs CNN vs RNN | Types of Neural Networks.” Analytics Vidhya, 17 Feb. 2020, [https://www.analyticsvidhya.com/blog/2020/02/cnn-vs-rnn-vs-mlp-analyzing-3-types-of-neural-networks-in-deep-learning/.]
*3Blue1Brown. But What Is a Neural Network? | Deep Learning, Chapter 1. 2017.YouTube, [https://www.youtube.com/watch?v=aircAruvnKk.]
*What Is Backpropagation Really Doing? | Deep Learning, Chapter 3. 2017. YouTube, [https://www.youtube.com/watch?v=Ilg3gGewQ5U&list=PLZHQObOWTQDNU6R1_67000Dx_ZCJB-3pi&index=3.]
*PyTorch Tutorials: beginner Data Parallel [https://pytorch.org/tutorials/beginner/blitz/data_parallel_tutorial.html]
*PyTorch Tutorials: Intermediate Model Parallel [https://pytorch.org/tutorials/intermediate/model_parallel_tutorial.html]
*Building our Neural Network - Deep Learning and Neural Networks with Python and Pytorch p.3, YouTube, [https://www.youtube.com/watch?v=ixathu7U-LQ]
*Training Model - Deep Learning and Neural Networks with Python and Pytorch p.4, YouTube, [https://www.youtube.com/watch?v=9j-_dOze4IM]
*Deep Learning with PyTorch: Building a Simple Neural Network| packtpub.com, YouTube, [https://www.youtube.com/watch?v=VZyTt1FvmfU&list=LL&index=4]
*Github PyTorch Neural Network Module Implementation [https://github.com/pytorch/pytorch/tree/master/torch/nn/modules]
*Project Jupyter Official Documentation [https://jupyter.org/documentation]
*PyTorch: Get Started [https://pytorch.org/get-started/locally/]
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