Comparison of deep learning frameworks from a viewpoint of double backpropagation
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Chainer Meetup #6@Preferred Networks, Inc. Japan in Sep. 30th 2017
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Comparison of deep learning frameworks from a viewpoint of double backpropagation
- 2. Agenda • Technological stack of DL frameworks • Design choice in DL frameworks • Double backprop primer • Coding examples of double backprop in Chainer, PyTorch, and TF 2
- 3. Technology stack of a DL framework name functions example Graphical visualization DIGITS, TensorBoard Machine learning workflow management Dataset prep, Save/Load Training loop Keras, TF slim Computational graph(CG) management Build/Optimize CGs Forward/Back prop Theano, TensorFlow Torch.nn Multi-dimensional array processing High-level array manipulation NumPy, CuPy Eigen, Torch (core) Numerical computation Matrix operation Convolution BLAS(OpenBLAS, MKL), cuBLAS, cuDNN, MKL DNN Computational device CPU, GPU, TPU, FPGA 3
- 4. Technology stack of Chainer cuDNN Chainer NumPy CuPy BLAS cuBLAS, cuRAND CPU GPU 4 name Graphical visualization Machine learning workflow management Computational graph management Multi-dimensional array processing Numerical computation Computational device
- 5. Technology stack of TensorFlow cuDNN TensorFlow Eigen::Tensor BLAS cuBLAS, cuRAND CPU GPU 5 TensorBoard TF slim Keras name Graphical visualization Machine learning workflow management Computational graph management Multi-dimensional array processing Numerical computation Computational device
- 6. Technology stack of Theano CUDA, OpenCL CUDAToolkit Theano BLAS CPU GPU 6 lib gpuarray NumPy Keras, Lasagne, Blocks, etc. name Graphical visualization Machine learning workflow management Computational graph management Multi-dimensional array processing Numerical computation Computational device
- 7. Technology stack of Keras 7 Keras TensorFlowTheano Technology Stack of Theano Technology Stack of TF name Graphical visualization Machine learning workflow management Computational graph management Multi-dimensional array processing Numerical computation Computational device
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- 15. Neural Network as a Computational Graph • In most frameworks, NN is conceptualized as a computational graph (CG). • The simplest form of CG is a bipartite DAG (Directed Acyclic Graph) consisting of data nodes and operator nodes. y = x1 * x2 z = y - x3 x1 mul suby x3 z x2 data node operator node 15
- 16. Multi Layer Perceptron (MLP) x Affine W1 b1 h1 ReLU a1 Affine W2 b2 h2 ReLU a2 Soft max prob Cross Entropy loss t 16
- 17. How to compute backprop Backprop through graphs Framework only builds graphs of forward prop, and do backprop by backtracking the graphs. E.g. Torch.nn, Caffe Backprop as extended graphs Framework builds graphs for backprop as well as those for forward prop. E.g. Theano, MXNet, TensorFlow, Chainer, PyTorch a mul suby c z b a mul suby c z b gzid neg mul mul gy gc ga gb ∇y z∇a z ∇z z = 1 17
- 19. Double backprop x F z y ・・・ L class F(FunctionNode): def forward(self, x, y): return x * x + y def backward(self, x, y, gz): return 2 * gz * x, gz NumPy, CuPy Note: The interface is simplified from actual implementation. chainer.Variable -> Creates CG 19
- 20. Double backprop x F z y gx Grad F gz gy ・・・ L Backprop! =∂L/∂z=∂L/∂x =∂L/∂y 1.0 =∂L/∂L Mul x gz y gx gy *2 20
- 21. Double backprop x F z y gx Grad F 1.0 gy Backprop! =∂z/∂x =∂z/∂y 21
- 22. Double backprop x F z y gx Grad F1.0 gy 22
- 23. Double backprop x Mul z y gx Grad F1.0 gy Backprop! 1.0 Double Grad F ggx =∂2z/∂x2 23
- 24. Double backprop x f z Computes the differentiation of L = G(f(x), ∇f(x)) with respect to x L = G(f(x), ∇f(x)) 24
- 25. Double backprop x f z gxGrad f Computes the differentiation of L = G(f(x), ∇f(x)) with respect to x L = G(f(x), ∇f(x)) 25
- 26. Double backprop x f z gxGrad f ・・・ L Computes the differentiation of L = G(f(x), ∇f(x)) with respect to x L = G(f(x), ∇f(x)) 26
- 27. Double backprop x f z gxGrad f ・・・ L Backprop! ggx Double Grad f ∂L/∂x 1.0gzGrad f Computes the differentiation of L = G(f(x), ∇f(x)) with respect to x L = G(f(x), ∇f(x)) 27
- 31. Conclusion • Several DL frameworks have similarity in their structure • Difference in choice of design determines capability of frameworks • Introduction of double backprop and toy examples in several frameworks. 31