Useful tools

Terry Benzschawel

This chapter presents several of the mathematical and statistical algorithms that underlie machine learning computation. Readers having no experience of logarithms, probability density distributions or regression will find this useful for understanding the concepts presented in subsequent chapters. Those familiar with these tools may wish to skip this chapter.

3.1 LOGARITHMS AND EXPONENTS

Consider first exponential functions. These are often used in the activation functions of artificial neurons. An exponential function is a mathematical expression in the form:

f(x)= a x (3.1) 

where x is a variable and a is a constant called the base of the function, which is typically greater than zero. A commonly used exponential function base is the transcendental number e, also called Euler’s number, which is approximately equal to 2.71828. The domain of an exponential function is the set of all real numbers; the range is the set of all positive real numbers. Another popular logarithmic base is 10.

Parts (a) and (b) of Figure 3.1 present examples of exponential growth and decay functions. As illustrated in the graph of the growth function f (x), the exponential function increases rapidly

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