If all entries outside the main diagonal are zero, A is called a diagonal matrix.
From the en.wikipedia.org
A superdiagonal entry is one that is directly above and to the right of the main diagonal.
From the en.wikipedia.org
Each row, column and main diagonal have the same totals.
From the newscientist.com
The off-diagonal entries are those not on the main diagonal.
From the en.wikipedia.org
The main diagonal of every adjacency matrix corresponding to a graph without loops has all zero entries.
From the en.wikipedia.org
We transform the matrix A into an upper triangular matrix U by eliminating the entries below the main diagonal.
From the en.wikipedia.org
The city has the shape of a square with a central park and two main diagonal avenues, north-south and east-west.
From the en.wikipedia.org
The box represents numbers 1 to 25 in some order in a magic square, where each row, column and main diagonal have the same sum.
From the newscientist.com
The letters in the diagram represent, in some order, the numbers 1 to 16 forming a magic square where each row, column and main diagonal have the same sum.