nullity
In linear algebra, the dimension of the null space (kernel) of a linear transformation or matrix; the number of linearly independent solutions to the homogeneous equation.
The nullity of a matrix can be calculated from its rank and the number of columns.
If the nullity is not zero, the linear transformation is not injective.
Rank (階数) is the dimension of the image, while nullity (退化次数) is the dimension of the kernel. Together they satisfy the rank-nullity theorem.
Null space (零空間) is the set of vectors mapped to zero; nullity (退化次数) is its dimension.
Compound of 退化 (degeneration, retrogression) and 次数 (degree, number of times). The term is a direct translation of the mathematical concept 'nullity'.