Transcription of Principal Components Analysis
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Chapter 18 Principal Components AnalysisPrincipal Components Analysis (PCA) is one of a family of techniques for takinghigh-dimensional data, and using the dependencies between the variables to representit in a more tractable, lower-dimensional form, without losing too much is one of the simplest and most robust ways of doing suchdimensionalityreduction. It is also one of the oldest, and has been rediscovered many times inmany fields, so it is also known as the Karhunen-Lo ve transformation, the Hotellingtransformation, the method of empirical orthogonal functions, and singular valuedecomposition1. We will call it Mathematics of Principal ComponentsWe start withp-dimensional vectors, and want to summarize them by projectingdown into aq-dimensional subspace.
we use q principal components, our weight matrix w will be a p ×q matrix, where each column will be a different eigenvector of the covariance matrix v. The eigen-values will give the total variance described by each component. The variance of the projections on to the first q principal components is then q i=1 λ i.
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