In mathematics, particularly linear algebra, a zero matrix or null matrix is a matrix all of whose entries are zero. It also serves as the additive identity of the additive group of m × n {\displaystyle m\times n} matrices, and is denoted by the symbol O {\displaystyle O} or 0 {\displaystyle 0} followed by subscripts corresponding to the dimension of the matrix as the context sees fit. Some examples of zero matrices are
0 1 , 1 = [ 0 ] , 0 2 , 2 = [ 0 0 0 0 ] , 0 2 , 3 = [ 0 0 0 0 0 0 ] . {\displaystyle 0_{1,1}={\begin{bmatrix}0\end{bmatrix}},\ 0_{2,2}={\begin{bmatrix}0&0\\0&0\end{bmatrix}},\ 0_{2,3}={\begin{bmatrix}0&0&0\\0&0&0\end{bmatrix}}.\ }
Properties The set of m × n {\displaystyle m\times n} matrices with entries in a ring K forms a ring K m , n {\displaystyle K_{m,n}} . The zero matrix 0 K m , n {\displaystyle 0_{K_{m,n}}\,} in K m , n {\displaystyle K_{m,n}\,} is the matrix with all entries equal to 0 K {\displaystyle 0_{K}\,} , where 0 K {\displaystyle 0_{K}} is the additive identity in K.
0 K m , n = [ 0 K 0 K ⋯ 0 K 0 K 0 K ⋯ 0 K ⋮ ⋮ ⋱ ⋮ 0 K 0 K ⋯ 0 K ] m × n {\displaystyle 0_{K_{m,n}}={\begin{bmatrix}0_{K}&0_{K}&\cdots &0_{K}\\0_{K}&0_{K}&\cdots &0_{K}\\\vdots &\vdots &\ddots &\vdots \\0_{K}&0_{K}&\cdots &0_{K}\end{bmatrix}}_{m\times n}}
The zero matrix is the additive identity in K m , n {\displaystyle K_{m,n}\,} . That is, for all A ∈ K m , n {\displaystyle A\in K_{m,n}\,} it satisfies the equation
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