a square matrix of any dimension whose elements are ones on its northwest-to-southeast diagonal and zeroes everywhere else

a square matrix with ones along the diagonal and zeros elsewhere

a trivial permutation matrix

Matrix embodying the null transformation that maps any vector to itself.

A scoring matrix in which only identical characters receive a positive score; the matrix has ones along the main diagonal and zeroes elsewhere.

In linear algebra, the identity matrix of size n is the n-by-n square matrix with ones on the main diagonal and zeros elsewhere. It is denoted by In, or simply by I if the size is immaterial or can be trivially determined by the context. (In some fields, such as quantum mechanics, the identity matrix is denoted by a boldface one, 1; otherwise it is identical to I.)