# Character table-equivalent groups

From Groupprops

This article defines an equivalence relation over the collection of groups. View a complete list of equivalence relations on groups.

## Definition

Suppose and are finite groups and is a splitting field in characteristic zero for both (we can take or . We say that and are **character table-equivalent groups** if there exists a bijection between the set of conjugacy classes in and that of , *and* a bijection between the set of irreducible characters (up to equivalence) of and that of , such that under this pair of bijections, the character table of is identified with that of . In other words, for any character of and any conjugacy class of , we have .

## Invariants

Character table-equivalent groups share a number of properties and arithmetic function values.

Invariant | Why it's the same for character table-equivalent groups |
---|---|

degrees of irreducible representations | These can be read off from the character table as the set of values that the character table takes at the identity element's conjugacy class. Note that the identity element's conjugacy class is the unique conjugacy class at which all character values are positive (this can be deduced from the column orthogonality theorem). |

order of the whole group | Follows from knowledge of degrees of irreducible representations, because sum of squares of degrees of irreducible representations equals order of group |

conjugacy class sizes | The size of each conjugacy class can be computed using the order and by computing its norm and using the column orthogonality theorem. |

order of derived subgroup (or equivalently, its index, which is the order of the abelianization) | use number of one-dimensional representations equals order of abelianization |

order of center | number of conjugacy classes of size 1. |

field generated by character values | The character table entries are the same, so the field they generate is the same. |

On the other hand, the following are not determined:

- Minimal splitting field: We could have two character table-equivalent groups such that they do not have isomorphic minimal splitting fields. For instance, dihedral group:D8 and quaternion group (see linear representation theory of dihedral group:D8 and linear representation theory of quaternion group).