A matrix is a two dimensional rectangular array of numbers with rows and columns (much like a spreadsheet or table of numbers). Matrix algebra is a shorthand method of writing complicated algebraic formulas. The use of matrix algebra greatly simplifies the explanation and calculation of many statistical methods such as regression, and is a necessity for explaining the prediction methods discussed in Chapters 4–12. In this chapter, we present a very brief and informal introduction to matrix algebra. We discuss only those topics needed for use in later chapters and therefore, this is by no means a complete introduction.
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