| Lower case j |
\(\underline{x}^j\) |
Number of coordinate of vector \(\underline{x}\) |
| Lower case i |
\(\underline{x}_i = (x^1_i, \dots, x^p_i)'\) |
Identify one specific observation of a (column) vector of the explanatory variables |
| Parenthesis to apply power |
\(\left( x_i^j \right)^2\) |
Denotes the power of the \(j\)-th variable for the \(i\)-th observation |
| Caligraphic J |
\(x^\mathcal{J}\) |
Denotes a subset of indices |
| Negative Mathematical J |
\(x^{-\mathcal{J}}\) |
Removing the \(j\)-th coordinate |
| \(=z\) |
\(\underline{x}^{j|=z}=(x^1, \dots, x^{j-1}, z, x^{j+1}, \dots, x^p)'\) |
Replaces the \(j\)-th component of vector \(\underline{x}\) with \(z\) |