the elements in a square matrix ranging from the upper left to the lower right corners of the matrix. Communality estimates are inserted in the main diagonal of a correlation matrix when performing a factor analysis. When performing a principal component analysis the main diagonal elements of the correlation matrix will be 1s.
the set of squares which bisect the board from corner to corner (a1 to h8 or a8 to h1) middle game the middle phase of the game, between the opening and endgame
In linear algebra, the main diagonal of a square matrix is the diagonal which runs from the top left corner to the bottom right corner.