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Stabilizer

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of an element $a$ in a set $M$

The subgroup $G_a$ of a group of transformations $G$, operating on a set $M$, (cf. Group action) consisting of the transformations that leave the element $a$ fixed: $G_a = \{ g \in G : ag = a \}$. The stabilizer of $a$ is also called the isotropy group of $a$, the isotropy subgroup of $a$ or the stationary subgroup of $a$. If $b \in M$ is in the orbit of $a$, so $b = af$ with $f \in G$, then $G_b = f^{-1}G_af$. If one considers the action of the group $G$ on itself by conjugation, the stabilizer of the element $g \in G$ will be the centralizer of this element in $G$; if the group acts by conjugation on the set of its subgroups, then the stabilizer of a subgroup $H$ will be the normalizer of this subgroup (cf. Normalizer of a subset).


Comments

In case $M$ is a set of mathematical structures, for instance a set of lattices in $\mathbf{R}^n$, on which a group $G$ acts, for instance the group of Euclidean motions, then the isotropy subgroup $G_m$ of $m \in M$ is the symmetry group of the structure $m \in M$.

References

[a1] L. Michel, "Simple mathematical models for symmetry breaking" K. Maurin (ed.) R. Raczka (ed.) , Mathematical Physics and Physical Mathematics , Reidel (1976) pp. 251–262
[a2] S. Helgason, "Differential geometry, Lie groups, and symmetric spaces" , Acad. Press (1978) pp. 121
[a3] T. Petrie, J.D. Randall, "Transformation groups on manifolds" , M. Dekker (1984) pp. 8, 9
How to Cite This Entry:
Stabilizer. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Stabilizer&oldid=38753
This article was adapted from an original article by N.N. Vil'yams (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article