---

Input matrix

A matrix with training features ²², as a rank-2 tensor:

\[\begin{equation*}
  X
  =
  \begin{pmatrix}
    \vphantom{\Big(}
    \vec{x}^1 & \cdots & \vec{x}^m
  \end{pmatrix}
  =
  \begin{pmatrix}
    x_1^1 & \cdots & x_1^m \\
    \vdots & \ddots & \vdots \\
    x_n^1 & \cdots & x_n^m
  \end{pmatrix}
  \in \mathbb{R}^{n \times m}
\end{equation*}
\]

where

• \(x^i\) is the \(i\)-th example
• \(x^i_j\) is the \(j\)-th feature of the \(i\)-th example

and

• \(m\) is the number of examples
• \(n\) is the number of features.