High Quality Content by WIKIPEDIA articles! An item in a matrix is called an entry or an element. In the example, e.g. 1 and 5 are entries. Entries are often denoted by a variable with two subscripts, as shown on the right. Matrices of the same size can be added and subtracted entrywise and matrices of compatible size can be multiplied. In matrix theory, a permutation matrix is a square (0,1)-matrix that has exactly one entry 1 in each row and each column and 0's elsewhere. Each such matrix represents a specific permutation of m elements and, when used to multiply another matrix, can produce that permutation in the rows or columns of the other matrix.