In linear algebra, the main diagonal (sometimes principal diagonal, primary diagonal, leading diagonal, major diagonal, or good diagonal) of a matrix
is the list of entries
where
. All off-diagonal elements are zero in a diagonal matrix. The following three matrices have their main diagonals indicated by red ones:
![{\displaystyle {\begin{bmatrix}\color {red}{1}&0&0\\0&\color {red}{1}&0\\0&0&\color {red}{1}\end{bmatrix}}\qquad {\begin{bmatrix}\color {red}{1}&0&0&0\\0&\color {red}{1}&0&0\\0&0&\color {red}{1}&0\end{bmatrix}}\qquad {\begin{bmatrix}\color {red}{1}&0&0\\0&\color {red}{1}&0\\0&0&\color {red}{1}\\0&0&0\end{bmatrix}}\qquad {\begin{bmatrix}\color {red}{1}&0&0&0\\0&\color {red}{1}&0&0\\0&0&\color {red}{1}&0\\0&0&0&\color {red}{1}\end{bmatrix}}\qquad }](https://wikimedia.org/api/rest_v1/media/math/render/svg/226359644d4df42b190b8d103be6b1f48c0b1cbf)
Antidiagonal
The antidiagonal (sometimes counter diagonal, secondary diagonal, trailing diagonal, minor diagonal, off diagonal, or bad diagonal) of an order
square matrix
is the collection of entries
such that
for all
. That is, it runs from the top right corner to the bottom left corner.
![{\displaystyle {\begin{bmatrix}0&0&\color {red}{1}\\0&\color {red}{1}&0\\\color {red}{1}&0&0\end{bmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/377690daa5dbe71d5a1e5cf14fbdefa672895527)
See also
References