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1 CS 4700: Foundations of Artificial Intelligence Prof. Bart Selman [email protected] Machine Learning: Neural Networks R&N 18.7 Backpropagation

CS 4700: Foundations of Artificial Intelligence...--- reinforcement learning (intro)--- neural networks / deep learning (gradient descent) The field has grown (and continues to grow)

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Page 1: CS 4700: Foundations of Artificial Intelligence...--- reinforcement learning (intro)--- neural networks / deep learning (gradient descent) The field has grown (and continues to grow)

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CS 4700:Foundations of Artificial Intelligence

Prof. Bart [email protected]

Machine Learning:Neural Networks

R&N 18.7Backpropagation

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Ok… details backpropagation NOT on exam.

But do work through gradient descent example on homework.

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It’s “just” multivariate (or multivariable) calculus.

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Optimizationandgradient descent.

Considerx and y ourtwo weightsand f(x,y)the errorsignal.

Multi-layernetwork:compositionof sigmoids;use chain rule.

Note:For descentwe want togo in oppositedirection ofgradient.

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Reminder:Gradient descent optimization.(Wikipedia)

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So, first we “backpropagate” the errorsignal to get the gradient, and then we update the weights, layer by layer.

That’s why it’s called “backprop learning.”Now changing speech recognition, imagerecognition etc.!

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Trace example!

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Etc.

Tedious but“just” gradientdescent in theweight space,after all.

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Bla bla

Wall Street Journal, 11/24/16

Good news…

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Summary J

A tour of AI:I) AI

--- motivation--- overview of the field

II) Problem-Solving–---- problem formulation using state space– (initial state, operators, goal state(s))–--- search techniques--- adversarial search

White white

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Summary, cont. III) Knowledge Representation and Reasoning

--- logical agents--- Boolean satisfiability (SAT) solvers--- first-order logic and inference

V) Learning–--- decision tree learning (info gain)--- reinforcement learning (intro)--- neural networks / deep learning (gradient descent)

The field has grown (and continues to grow) exponentially but youhave now seen a good part!

Thanks & Have a great winter break!!!!