mhjensen
58 lines
2.7 KiB
Plaintext
58 lines
2.7 KiB
Plaintext
{
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"<!-- dom:TITLE: Data Analysis and Machine Learning: Recurrent neural networks -->\n",
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"# Data Analysis and Machine Learning: Recurrent neural networks\n",
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"<!-- dom:AUTHOR: Morten Hjorth-Jensen at Department of Physics, University of Oslo & Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University -->\n",
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"<!-- Author: --> \n",
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"**Morten Hjorth-Jensen**, Department of Physics, University of Oslo and Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University\n",
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"\n",
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"Date: **Jan 8, 2019**\n",
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"\n",
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"Copyright 1999-2019, Morten Hjorth-Jensen. Released under CC Attribution-NonCommercial 4.0 license\n",
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"\n",
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"\n",
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"\n",
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"\n",
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"## Recurrent neural networks: Overarching view\n",
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"\n",
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"Till now our focus has been, including convolutional neural networks as well, \n",
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"on feedforward neural networks. The output or the\n",
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"activations flow only in one direction, from the input layer to the\n",
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"output layer.\n",
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"\n",
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"A recurrent neural network (RNN) looks very much like a feedforward\n",
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"neural network, except that it also has connections pointing\n",
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"backward. \n",
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"\n",
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"RNNs are used to analyze time series data such as stock prices, and\n",
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"tell you when to buy or sell. In autonomous driving systems, they can\n",
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"anticipate car trajectories and help avoid accidents. More generally,\n",
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"they can work on sequences of arbitrary lengths, rather than on\n",
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"fixed-sized inputs like all the nets we have discussed so far. For\n",
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"example, they can take sentences, documents, or audio samples as\n",
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"input, making them extremely useful for natural language processing\n",
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"systems such as automatic translation and speech-to-text.\n",
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"\n",
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"\n",
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"## Set up of an RNN\n",
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"\n",
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"The figure here displays a simple example of an RNN, with inputs $x_t$\n",
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"at a given time $t$ and outputs $y_t$. Introducing time as a variable\n",
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"offers an intutitive way of understanding these networks. In addition\n",
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"to the inputs $x_t$, the layer at a time $t$ receives also as input\n",
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"the output from the previous layer $t-1$, that is $y_{t1}$.\n",
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"\n",
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"This means also that we need to have weights that link both the inputs $x_t$ to the outputs $y_t$ as well as weights that link\n",
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"the output from the previous time $y_{t-1}$ and $y_t$. The figure here shows an example of a simple RNN."
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