ML unit-2 Notes

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This document provides an overview of Artificial Neural Networks (ANNs), focusing on their representations, learning algorithms, and related concepts in Machine Learning. ANNs offer a general, practical method for learning real-valued, discrete-valued, and vector-valued functions from examples and are inspired by biological neural systems.

The core building block, the perceptron, calculates a weighted linear combination of inputs and outputs a binary value. Key learning rules discussed are the Perceptron Rule and the Delta Rule. The Perceptron Rule iteratively adjusts weights to correctly classify linearly separable examples. The Delta Rule, designed to overcome the linear separability limitation, uses gradient descent to minimize a squared error function for unthresholded units. For multilayer networks, the Backpropagation algorithm, which employs Stochastic Gradient Descent (SGD) with sigmoid units, is introduced as a method capable of learning non-linear decision surfaces. The notes also cover methods for estimating hypothesis accuracy, including True Error, Sample Error, and Confidence Intervals.

Here are 5 key topics covered:
  • Artificial Neural Networks (ANNs): A general, practical method for learning various types of functions from examples, inspired by biological learning systems built of interconnected neurons.
  • Perceptrons: The basic unit of an ANN that takes real-valued inputs, computes a linear combination of these inputs, and outputs 1 or -1 based on whether the result exceeds a threshold.
  • Backpropagation Algorithm: A commonly used technique for training multilayer networks with sigmoid units, which employs Stochastic Gradient Descent (SGD) to minimize the squared error between network outputs and target values.
  • Delta Rule: A learning algorithm that uses gradient descent to search for the weight vector that best fits the training examples, designed to overcome the limitation of the perceptron rule in cases where training examples are not linearly separable.
  • Hypothesis Accuracy Estimation: Concepts and methods, such as True Error and Sample Error, used to estimate the accuracy of a learned hypothesis, including the use of Confidence Intervals to quantify the probable error in the estimate.

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