Notation

Description	Example	Meaning
\(*j\)	\(\underline{X}^{*j}\)	Denote a matrix with the values as \(\underline{X}\) except of \(j\)-th which elements are permuted
Model residual	\(r_i = y_i - f(x_i)\) \(r_i = y_i - \hat{y}_i\)	The difference between the observed value of the dependent variable \(Y\) for the \(i\)-th observation and the model’s prediction for that observation