In mathematics, an element of a ring is called nilpotent if there exists some positive integer , called the index (or sometimes the degree), such that .

The term, along with its sister idempotent, was introduced by Benjamin Peirce in the context of his work on the classification of algebras.[1]


  • This definition can be applied in particular to square matrices. The matrix
is nilpotent because  . See nilpotent matrix for more.
  • In the factor ring  , the equivalence class of 3 is nilpotent because 32 is congruent to 0 modulo 9.
  • Assume that two elements   and   in a ring   satisfy  . Then the element   is nilpotent as   An example with matrices (for ab):  Here   and  .



No nilpotent element can be a unit (except in the trivial ring, which has only a single element 0 = 1). All nilpotent elements are zero divisors.

An   matrix   with entries from a field is nilpotent if and only if its characteristic polynomial is  .

If   is nilpotent, then   is a unit, because   entails  

More generally, the sum of a unit element and a nilpotent element is a unit when they commute.

Commutative rings


The nilpotent elements from a commutative ring   form an ideal  ; this is a consequence of the binomial theorem. This ideal is the nilradical of the ring. Every nilpotent element   in a commutative ring is contained in every prime ideal   of that ring, since  . So   is contained in the intersection of all prime ideals.

If   is not nilpotent, we are able to localize with respect to the powers of  :   to get a non-zero ring  . The prime ideals of the localized ring correspond exactly to those prime ideals   of   with  .[2] As every non-zero commutative ring has a maximal ideal, which is prime, every non-nilpotent   is not contained in some prime ideal. Thus   is exactly the intersection of all prime ideals.[3]

A characteristic similar to that of Jacobson radical and annihilation of simple modules is available for nilradical: nilpotent elements of ring   are precisely those that annihilate all integral domains internal to the ring   (that is, of the form   for prime ideals  ). This follows from the fact that nilradical is the intersection of all prime ideals.

Nilpotent elements in Lie algebra


Let   be a Lie algebra. Then an element   is called nilpotent if it is in   and   is a nilpotent transformation. See also: Jordan decomposition in a Lie algebra.

Nilpotency in physics


Any ladder operator in a finite dimensional space is nilpotent. They represent creation and annihilation operators, which transform from one state to another, for example the raising and lowering Pauli matrices  .

An operand   that satisfies   is nilpotent. Grassmann numbers which allow a path integral representation for Fermionic fields are nilpotents since their squares vanish. The BRST charge is an important example in physics.

As linear operators form an associative algebra and thus a ring, this is a special case of the initial definition.[4][5] More generally, in view of the above definitions, an operator   is nilpotent if there is   such that   (the zero function). Thus, a linear map is nilpotent iff it has a nilpotent matrix in some basis. Another example for this is the exterior derivative (again with  ). Both are linked, also through supersymmetry and Morse theory,[6] as shown by Edward Witten in a celebrated article.[7]

The electromagnetic field of a plane wave without sources is nilpotent when it is expressed in terms of the algebra of physical space.[8] More generally, the technique of microadditivity (which can used to derive theorems in physics) makes use of nilpotent or nilsquare infinitesimals and is part smooth infinitesimal analysis.

Algebraic nilpotents


The two-dimensional dual numbers contain a nilpotent space. Other algebras and numbers that contain nilpotent spaces include split-quaternions (coquaternions), split-octonions, biquaternions  , and complex octonions  . If a nilpotent infinitesimal is a variable tending to zero, it can be shown that any sum of terms for which it is the subject is an indefinitely small proportion of the first order term.

See also



  1. ^ Polcino Milies & Sehgal (2002), An Introduction to Group Rings. p. 127.
  2. ^ Matsumura, Hideyuki (1970). "Chapter 1: Elementary Results". Commutative Algebra. W. A. Benjamin. p. 6. ISBN 978-0-805-37025-6.
  3. ^ Atiyah, M. F.; MacDonald, I. G. (February 21, 1994). "Chapter 1: Rings and Ideals". Introduction to Commutative Algebra. Westview Press. p. 5. ISBN 978-0-201-40751-8.
  4. ^ Peirce, B. Linear Associative Algebra. 1870.
  5. ^ Polcino Milies, César; Sehgal, Sudarshan K. An introduction to group rings. Algebras and applications, Volume 1. Springer, 2002. ISBN 978-1-4020-0238-0
  6. ^ A. Rogers, The topological particle and Morse theory, Class. Quantum Grav. 17:3703–3714, 2000 doi:10.1088/0264-9381/17/18/309.
  7. ^ E Witten, Supersymmetry and Morse theory. J.Diff.Geom.17:661–692,1982.
  8. ^ Rowlands, P. Zero to Infinity: The Foundations of Physics, London, World Scientific 2007, ISBN 978-981-270-914-1