383-Fall11-Lec20 - Articial Neural Networks" and...

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1 CMPSCI 383 Nov 17, 2011 Artifcial Neural Networks and Nonparametric Methods
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2 Today ʼ s lecture How the brain works (!) Artifcial neural networks Perceptrons Multilayer Feed-Forward networks Error backpropagation algorithm Nonparametric methods Nearest neighbor models Nonparametric regression
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3 How the brain works Remains a great mystery of science! Basic component: the neuron.
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4 The brain and the digital computer Even though a computer is a million times faster in raw switching speed, the brain ends up being a billion times faster at what it does. “Massive parallelism”
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5 Artifcial Neural Networks Also called: neural networks, connectionist systems, neuromorphic systems, parallel distributed processing (PDP) systems, etc. Networks of relatively simple processing units, which are very abstract models of neurons; the network does the computation more than the units.
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6 Neuron-like units j i w i , j
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7 Typical activation functions
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8 A useful trick a j = step t ( w i , j a i ) i = 1 n = step 0 ( w i , j a i ) i = 0 n where w 0, j = t a 0 = 1 So we can always assume a threshold of 0 if we add an extra input always equal to –1
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383-Fall11-Lec20 - Articial Neural Networks" and...

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