Question

what is a diagonal matrix? with example

Answer 1

a matrix having non-zero elements only in the diagonal running from the upper left to the lower right.

Answer 2

$diagonal \: matrix \\ in \: linear \: algebra \: \: it \: is \: a \: matrix \: in \: which \: entries \: outside \: the \: main \: diagonal \: are \: all \: 0. \\ example \:$

A 2 × 2 matrix
( 2. 0 )
( 0. 1) is a diagonal matrix.