noun
triangular matrix
A square matrix where all entries above or below the main diagonal are zero. Used in linear algebra.
三角行列の行列式は対角成分の積に等しい。
The determinant of a triangular matrix equals the product of its diagonal entries.
A diagonal matrix is a special case of a triangular matrix where both the upper and lower off-diagonal entries are zero.
Compound of 三角 (さんかく, 'triangle') and 行列 (ぎょうれつ, 'matrix'), referring to the triangular shape of the non-zero entries.