Main diagonal

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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:


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.

See also[edit]


  • Weisstein, Eric W. "Main diagonal". MathWorld.