Appendix B — Math Terms

Math terms used throughout this book:

Math Term	Meaning
\(X_j\)	Random variable corresponding to feature \(j\).
\(X\)	Set of all random variables.
\(\mathbb{P}\)	Probability measure.
\(\mathbb{P}(X_j = c)\)	Probability that random variable \(X_j\) takes on the value \(c\).
\(\mathbf{x}_j\)	Vector of values for feature \(j\) across multiple data instances.
\(\mathbf{x}^{(i)}\)	Feature vector of the \(i\)-th instance.
\(x^{(i)}_j\)	Value of feature \(j\) for the \(i\)-th instance.
\(y^{(i)}\)	Target value for the \(i\)-th instance.
\(\mathbf{X}\)	Feature matrix, where rows correspond to instances and columns to features.
\(\mathbf{y}\)	Vector of target values, one for each instance.
\(n\)	Number of data instances (rows in \(\mathbf{X}\)).
\(p\)	Number of features (columns in \(\mathbf{X}\)).