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Short story assignment - Deep Learning

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- Short Story Submission Rimzim Thube SJSU ID- 014555021
- A Survey of Convolutional Neural Networks: Analysis, Applications, and Prospects Zewen Li, Wenjie Yang, Shouheng Peng, Fan Liu, Member, IEEE
- Introduction to Convolution Neural Network (CNN) •Applications using CNN – •Face recognition •Autonomous vehicles •Self-service supermarket •Intelligent medical treatment
- Emergence of CNN • McCulloch and Pitts – First mathematical MP model of neurons • Rosenblatt - Added learning capability to MP model • Hinton – Proposed multi-layer feedforward network trained by the error Back Propagation – BP network • Waibel - Time Delay Neural Network (TDNN) for speech recognition • LeCun – First convolution network (LeNet) to recognize handwritten text
- Overview of CNN • Feedforward neural network • Extracts features from data from convolution structures • Architecture inspired by visual perception • Biological neuron corresponds to an artificial neuron • CNN kernels represent different receptors that can respond to various features • Activation function transmit signal to next neuron if it exceeds certain threshold • Loss functions and optimizers teach the whole CNN system to learn
- Advantages of CNN • Local connections – Each neuron connected to not all but small no. of neurons. Reduces parameters and speed up convergence. • Weight sharing - Connections share same weights • Down-sampling dimensionality reduction. • These characteristics make CNN most representative algorithms
- Components of CNN • Convolution - pivotal step for feature extraction. Output is feature map • Padding - introduced to enlarge the input with zero value • Stride – Control the density of convolution • Pooling - Obviate redundancy or down sampling
- LeNet - 5 • Composed of 7 trainable layers containing 2 convolutional layers, 2 pooling layers, and 3 fully-connected layers • NN characteristics of local receptive fields, shared weights, and spatial or temporal subsampling, ensures shift, scale, and distortion • Used for handwriting recognition
- AlexNet • Has 8 layers, containing 5 convolutional layers and 3 fully-connected layers • uses ReLU as the activation function of CNN to solve gradient vanishing • Dropout was used in last few layers to avoid overfitting • Local Response Normalization (LRN) to enhance generalization of model
- AlexNet • Employ 2 powerful GPUs, two feature maps generated by two GPUs can be combined as the final output • Enlarges dataset and calculates average of their predictions as final result • Principal Component Analysis (PCA) to change the RGB values of training set
- VGGNet • LRN layer was removed • VGGNets use 3 × 3 convolution kernels rather than 5 × 5 or 5 × 5 ones, since several small kernels have the same receptive field and more nonlinear variations compared with larger ones.
- GoogLeNet - Inception v1 • CNN formed by stacking with Inception modules • Inception v1 deploys 1 × 1, 3 × 3, 5 × 5 convolution kernels to construct a “wide” network • Convolution kernels with different sizes can extract the feature maps of different scales of the image • 1 × 1 convolution kernel is used to reduce the number of channels, i.e., reduce computational cost
- GoogLeNet - Inception v2 • Output of every layer is normalized to increase the robustness of model and train it with high learning rate • Single 5 × 5 convolutional layers can be replaced by two 3 × 3 ones • One n x n convolutional layer can be replaced byone 1 x n and one n x 1 convolutional layer • Filter banks expanded wider to improve high dimensional representations
- ResNet • Two layer residual block constructed by the shortcut connection • 50-layer ResNet, 101-layer ResNet, and 152-layer ResNet utilize three- layer residual blocks • Three-layer residual block is also called the bottleneck module because the two ends of the block are narrower than the middle • Can mitigate the gradient vanishing problem since the gradient can directly flow through shortcut connections •
- DCGAN • GAN has generative model G and a discriminative model D • The model G with random noise z generates a sample G(z) that subjects to the data distribution data learned by G. • The model D can determine whether the input sample is real data x or generated data G(z). • Both G and D can be nonlinear functions. The aim of G is to generate real data, the aim of D is to distinguish fake data generated by G from the real data
- MobileNets • lightweight models proposed by Google for embedded devices such as mobile phones • depth-wise separable convolutions and several advanced techniques to build thin deep neural networks.
- ShuffleNets • Series of CNN-based models to solve the problem of insufficient computing power of mobile devices • Combine pointwise group convolution, channel shuffle, which significantly reduce the computational cost with little loss of accuracy
- GhostNet • As large amounts of redundant features are extracted by existing CNNs for image cognition, GhostNet is used to reduce computational cost effectively • Similar feature maps in traditional convolution layers are called ghost • Traditional convolution layers divided into two parts • Less convolution kernels are directly used in feature extraction • These features are processed in linear transformation to acquire multiple feature maps. They proved that Ghost module applies to other CNN models
- Activation function • In a multilayer neural network, there is a function between two layers which is called activation function • Determines which information should be transmitted to the next neuron • If no activation function, input layer will be linear function of the output • Nonlinear functions are introduced as activation functions to enhance ability of neural network
- Types of activation function • Sigmoid function can map a real number to (0, 1), so it can be used for binary classification problems. • Tanh function maps a real number to (-1, 1), achieves normalization. This makes the next layer easier to learn. • Rectified Linear Unit (ReLU), when x is less than 0, its value is 0; when x is greater than or equal to 0, its value is x itself. Speeds up learning. • ELU function has a negative value, so the average value of its output is close to 0, making the rate of convergence faster than ReLU.
- Loss/Cost function • Calculates the distance between the predicted value and the actual value • Used as a learning criterion of the optimization problem • Common loss functions Mean Absolute Error (MAE), Mean Square Error (MSE), Cross Entropy
- Rules of Thumb for Loss Function Selection • CNN models for regression problems, choose L1 loss or L2 loss as the loss function. • For classification problems, select the rest of the loss functions • Cross entropy loss is the most popular choice, with a softmax layer in the end. • The selection of loss function in CNNs also depends on the application scenario. For example, when it comes to face recognition, contrastive loss and triplet loss are turned out to be the commonly- used ones nowadays.
- Optimizer • In convolutional neural networks, need to optimize non-convex functions. • Mathematical methods require huge computing power, so optimizers are used in the training process to minimize the loss function for getting optimal network parameters within acceptable time. • Common optimization algorithms are Momentum, RMSprop, Adam, etc.
- Applications of one-dimensional CNN • Time Series Prediction • Electrocardiogram (ECG) time series, weather forecast, and traffic flow prediction, highway traffic flow prediction • Signal Identification • ECG signal identification, structural damage identification, and system fault identification
- Applications of two-dimensional CNN • Image Classification • medical image classification, traffic scenes related classification, classify breast cancer tissues • Object Detection • Image Segmentation • Face Recognition
- Applications of multi-dimensional CNN • Human Action Recognition • Object Recognition/Detection
- Conclusion • Due to the advantages of convolutional neural networks, such as local connection, weight sharing, and down-sampling dimensionality reduction, they have been widely deployed in both research and industry projects • First, we discussed basic building blocks of CNN and how to construct a CNN-based model from scratch • Secondly, some excellent CNN networks • Third, we introduce activation functions, loss functions, and optimizers for CNN • Fourth, we discuss some typical applications of CNN • CNN can be refined further in terms of model size, security, and easy hyperparameters selection. Moreover, there are lots of problems that convolution is hard to handle, such as low generalization ability, lack of equivariance, and poor crowded-scene results, so that several promising directions are pointed.