Special Matrices

1. A square matrix has the same number of rows as columns.
   • This means that, if $n$ is the number of rows (and columns), then the size of a square matrix is $n \times n$
   • We denote a square matrix $A$ as $A_{n \times n}$. Morever, since the number of rows and columns is equal, we can conveniently use the shorthand notation: $A_n$ (

     $A_n$

     ).
   
   Examples:

   3. $S_1 = \begin{bmatrix} \text{Bla} \end{bmatrix}$

   6. $I_4 = \begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \end{bmatrix}$

   8. $N_3 = \begin{bmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{bmatrix}$

   14. $M_3 = \begin{bmatrix} 0 & 1 & 2 \\ 1 & 2 & 3 \\ 2 & 3 & 4 \end{bmatrix}$

   17. $D_2 = \begin{bmatrix} a & b \\ c & d \end{bmatrix}$