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Building high-level features using large-scale unsupervised learning Anh Nguyen, Bay-yuan Hsu CS290D – Data Mining (Spring 2014) University of California, Santa Barbara Slide adapted from Andrew Ng (Stanford), Nando de Freitas (UBC) 1
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Agenda 1.Motivation 2.Approach 1.Sparse Deep Auto-encoder 2.Local Receptive Field 3.L2 Pooling 4.Local contrast normalization 5.Overall Model 3.Parallelism 4.Evaluation 5.Discussion 2
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1. MOTIVATION 3
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Motivation Feature learning Supervised learning Need large number of labeled data Unsupervised learning Example: Build face detector without having labeled face images Building high-level features using unlabeled data. 4
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Motivation Previous works Auto encoder Sparse coding Result: Only learns low level features Reason: Computational constraints Approach Dataset Model Computational resources 5
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2. APPROACH 6
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Sparse Deep Auto-encoder Auto-encoder Neural network Unsupervised learning Back-propagation 7
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Sparse Deep Auto-encoder (cnt’d) Sparse Coding Input: Images x (1), x (2)... x (m) Learn: Bases (features) f 1, f 2,..., f k, so that each input x can be approximately decomposed as: x=∑a j f j s.t. a j ’s are mostly zero (“sparse”) 8
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Sparse Deep Auto-encoder (cnt’d) 9
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Sparse Coding Regularizer 10
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Sparse Deep Auto-encoder (cnt’d) Sparse Deep Auto-encoder Multiple hidden layers to achieve particular characteristic in learning features 11
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Local Receptive Field Definition: Each feature in the autoencoder can connect only to a small region of the lower layer Goal: Learn feature efficiently Parallelism Training on small image patches 12
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L2 Pooling Goal: Robust to local distortion Approach: Group similar features together to achieve invariance 13
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L2 Pooling Goal: Robust to local distortion Approach: Group similar features together to achieve invariance 14
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L2 Pooling Goal: Robust to local distortion Approach: Group similar features together to achieve invariance 15
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L2 Pooling Goal: Robust to local distortion Approach: Group similar features together to achieve invariance 16
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Local Contrast Normalization Goal: Robust to variation in light intensity Approach: Normalize contrast 17
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Local Contrast Normalization Goal: Robust to variation in light intensity Approach: Normalize contrast 18
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Overall Model 3 layers Simple: 18x18 px 8 neurons/patch Complex: 5x5 px LCN: 5x5 px 19
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Overall Model 20
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Overall Model Train: Reconstruct input of each layer Optimization function 21
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Overall Model Complex model? 22
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3. PARALLELISM 23
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Asynchronous SGD Two recent lines of research in speeding up large learning problems: Parallel/distributed computing Online (and mini-batch) learning algorithms: stochastic gradient descent, perceptron, MIRA, stepwise EM How can we bring together the benefits of parallel computing and online learning? 24
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Asynchronous SGD SGD: Stochastic Gradient Descent: Choose an initial vector of parameters W and learning rate α Repeat until an approximate minimum is obtained: Randomly shuffle examples in the training set 25
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Model Parallelism Weights divided according to locality of image and store on different machine 29
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5. EVALUATION 30
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Evaluation 10M Youtube unlabeled frames of size 200x200 1B parameters 1000 machines 16,000 cores 31
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Experiment on Faces Test set 37,000 images 13,026 face images Best neuron 32
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Experiment on Faces (cnt’d) Visualization Top stimulus (images) for face neuron Optimal stimulus for face neuron 33
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Experiment on Faces (cnt’d) Invariances Properties 34
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Experiment on Faces (cnt’d) Invariances Properties 35
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Experiment on Cat/Human body Test set Cat: 10,000 positive, 18,409 negative Human body: 13,026 positive, 23,974 negative Accuracy 36
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ImageNet classification Recognizing images Dataset 20,000 categories 14M images Accuracy 15.8% State of art: 9.3% 37
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5. DISCUSSION 38
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Discussion Deep learning Unsupervised feature learning Learning multiple layers of representation Increase accuracy: Invariance, contrast normalization Scalability 39
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6. REFERENCES 40
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References 1.Quoc Le et al., “Building High-level Features using Large Scale Unsupervised Learning” 2.Nando de Freitas, “Deep Learning”, URL: https://www.youtube.com/watch?v=g4ZmJJWR34Q 3.Andrew Ng, “Sparse autoencoder”, URL: http://www.stanford.edu/class/archive/cs/cs294a/cs294a.1104/sparseAutoencod er.pdf 4.Andrew Ng, “Machine Learning and AI via Brain Simulations”, URL: https://forum.stanford.edu/events/2011slides/plenary/2011plenaryNg.pdf 5.Andrew Ng, “Deep Learning”, URL: http://www.ipam.ucla.edu/publications/gss2012/gss2012_10595.pdf 41
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