In linear algebra, the main diagonal (sometimes principal diagonal, primary diagonal, leading diagonal, or major diagonal) of a matrix A is the collection of entries A i , j where i = j . All off-diagonal elements are zero in a diagonal matrix. The following three matrices have their main diagonals indicated by red 1's:
[ 1 0 0 0 1 0 0 0 1 ] [ 1 0 0 0 0 1 0 0 0 0 1 0 ] [ 1 0 0 0 1 0 0 0 1 0 0 0 ] The antidiagonal (sometimes counterdiagonal, secondary diagonal, trailing diagonal or minor diagonal) of a dimension N square matrix, B , is the collection of entries B i , j such that i + j = N + 1 . That is, it runs from the top right corner to the bottom left corner:
[ 0 0 1 0 1 0 1 0 0 ] 