Main diagonal

In linear algebra, the main diagonal (sometimes principal diagonal, primary diagonal, leading diagonal, or major diagonal) of a matrix A {displaystyle A} is the collection of entries A i , j {displaystyle A_{i,j}} where i = j {displaystyle 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: In linear algebra, the main diagonal (sometimes principal diagonal, primary diagonal, leading diagonal, or major diagonal) of a matrix A {displaystyle A} is the collection of entries A i , j {displaystyle A_{i,j}} where i = j {displaystyle 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: The antidiagonal (sometimes counter diagonal, secondary diagonal, trailing diagonal, minor diagonal, or bad diagonal) of a dimension N {displaystyle N} square matrix, B {displaystyle B} , is the collection of entries B i , j {displaystyle B_{i,j}} such that i + j = N + 1 {displaystyle i+j=N+1} for all 1 ≤ i , j ≤ N {displaystyle 1leq i,jleq N} . That is, it runs from the top right corner to the bottom left corner: