A block matrix is an m × n {\displaystyle {}m\times n} -matrix of the form
where A {\displaystyle {}A} is an r × s {\displaystyle {}r\times s} -matrix, B {\displaystyle {}B} is an r × ( n − s ) {\displaystyle {}r\times (n-s)} -matrix, C {\displaystyle {}C} is an ( m − r ) × s {\displaystyle {}(m-r)\times s} -matrix and D {\displaystyle {}D} is an ( m − r ) × ( n − s ) {\displaystyle {}(m-r)\times (n-s)} -matrix.
