An element of a ring is nilpotent when for some positive integer . A field has no nonzero nilpotent elements.
An element of an associative algebra is square-zero if its square vanishes. Every such element is a nilpotent element. These elements are preserved by an algebra isomorphism, so their structure distinguishes algebras. Their set need not be a vector space: the matrix units and are square-zero, while their sum has square equal to the identity in . In a square-zero ideal, by contrast, every pairwise product vanishes and all its elements are square-zero. In the square-zero elements are exactly the multiples of , over every field: forces .
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In mathematics, particularly in the study of linear algebra and abstract algebra, the term "nilpotent" refers to a specific type of element in a ring or algebra. An element \( a \) of a ring \( R \) is said to be nilpotent if there exists a positive integer \( n \) such that \[ a^n = 0. \] In this context, \( 0 \) represents the additive identity in the ring \( R \).