Mathematics > algebra > Matrices

$a_{ij} = 0, \forall i, j$

$a_{ij} = \begin{cases} 0, & \text{if } i \ne j \\ 1, & \text{if } i=j \end{cases}$

$a_{ij} = \begin{cases} 0, & \text{if } i=j \\ 1, & \text{if } i \ne j \end{cases}$

$a_{ij} = 1, \forall i, j$