DiagonalMatrixQ¶

True if a matrix is diagonal.

$ wo 'DiagonalMatrixQ[{{1, 2}, {0, 3}}]'
False

DiagonalMatrixQ[m, k] tests whether the nonzero entries lie only on the k-th diagonal (positive k for super-, negative for sub-diagonals).

$ wo 'DiagonalMatrixQ[{{0, 1, 0}, {0, 0, 1}, {0, 0, 0}}, 1]'
True

Rectangular matrices are accepted.

$ wo 'DiagonalMatrixQ[{{1, 0, 0}, {0, 2, 0}}]'
True

A non-matrix argument (scalar, symbol, vector) is not diagonal.

$ wo 'DiagonalMatrixQ[5]'
False