Namespaces
Variants
Actions

Difference between revisions of "Annihilator"

From Encyclopedia of Mathematics
Jump to: navigation, search
(supplement on linear spaces)
(→‎Modules: annihilator of an element, cite Bourbaki, Lang (2002))
(One intermediate revision by the same user not shown)
Line 14: Line 14:
 
is the two-sided annihilator of $X$. In an associative ring (or semi-group) $R$ the left annihilator of an arbitrary set $X$ is a left ideal, and if $X$ is a left ideal of $R$, then $\mathfrak{Z}_l(X)$ is a two-sided ideal of $R$; in the non-associative case these statements are usually not true.
 
is the two-sided annihilator of $X$. In an associative ring (or semi-group) $R$ the left annihilator of an arbitrary set $X$ is a left ideal, and if $X$ is a left ideal of $R$, then $\mathfrak{Z}_l(X)$ is a two-sided ideal of $R$; in the non-associative case these statements are usually not true.
  
 +
===Modules===
 +
Let $M$ be a left module over a ring $R$, and $X$ a subset of $M$.  The left annihilator of $X$ is 
 +
$$
 +
\mathfrak{Z}_l(X) = \{ z \in R : Xz = \{0\} \} \ .
 +
$$
 +
Again, the left annihilator of an arbitrary set $X$ is a left ideal.  The annihilator of an element $x \in M$ is the annihilator of $\{ x \}$.  As left $R$-modules we have
 +
$$
 +
R/\mathfrak{Z}_l(\{x\}) \cong Rx \ .
 +
$$
 +
 +
====References====
 +
<table>
 +
<TR><TD valign="top">[a1]</TD> <TD valign="top">  N. Bourbaki,  "Algebra I" , Springer  (1998) ISBN 3-540-64243-9</TD></TR>
 +
<TR><TD valign="top">[a2]</TD> <TD valign="top">  N. Bourbaki,  "Algebra II" , Springer  (2003) ISBN 3-540-00706-7</TD></TR>
 +
<TR><TD valign="top">[a3]</TD> <TD valign="top">  S. Lang,  "Algebra" , Springer  (2002) ISBN 0-387-95385-X</TD></TR>
 +
</table>
  
 
===Linear spaces===
 
===Linear spaces===

Revision as of 16:48, 1 November 2014


left, of a set $X$ in $R$

The set $\mathfrak{Z}_l(X)$ of all elements $y$ in $R$ such that $yX = \{0\}$. Here $R$ is a ring or a semi-group (or, generally, a groupoid) with a zero. The right annihilator of a set $X$ in $R$ is defined in a similar manner as the set $$ \mathfrak{Z}_r(X) = \{ z \in R : Xz = \{0\} \} \ . $$

The set $$ \mathfrak{Z}(X) = \mathfrak{Z}_l(X) \cap \mathfrak{Z}_r(X) $$ is the two-sided annihilator of $X$. In an associative ring (or semi-group) $R$ the left annihilator of an arbitrary set $X$ is a left ideal, and if $X$ is a left ideal of $R$, then $\mathfrak{Z}_l(X)$ is a two-sided ideal of $R$; in the non-associative case these statements are usually not true.

Modules

Let $M$ be a left module over a ring $R$, and $X$ a subset of $M$. The left annihilator of $X$ is $$ \mathfrak{Z}_l(X) = \{ z \in R : Xz = \{0\} \} \ . $$ Again, the left annihilator of an arbitrary set $X$ is a left ideal. The annihilator of an element $x \in M$ is the annihilator of $\{ x \}$. As left $R$-modules we have $$ R/\mathfrak{Z}_l(\{x\}) \cong Rx \ . $$

References

[a1] N. Bourbaki, "Algebra I" , Springer (1998) ISBN 3-540-64243-9
[a2] N. Bourbaki, "Algebra II" , Springer (2003) ISBN 3-540-00706-7
[a3] S. Lang, "Algebra" , Springer (2002) ISBN 0-387-95385-X

Linear spaces

Let $V$ be a vector space over a field $K$ and $V^*$ the dual space of linear functional‎s on $V$. For a subset $X$ of $V$, the annihilator $$ X^\circ = \{ f \in V^* : f(X) = \{0\} \} \ . $$ The annihilator of a general set $X$ is a subspace of $V^*$ and if $\langle X \rangle$ is the subspace of $V$ generated by $X$, then $X^\circ = \langle X \rangle^\circ$.

How to Cite This Entry:
Annihilator. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Annihilator&oldid=34141
This article was adapted from an original article by K.A. Zhevlakov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article