mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...

, a multiplicative character (or linear character, or simply character) on a group ''G'' is a group homomorphism from ''G'' to the multiplicative group of a

field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grass ...

, usually the field of complex numbers. If ''G'' is any group, then the

set Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements *Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electro ...

Ch(''G'') of these morphisms forms an

abelian group In mathematics, an abelian group, also called a commutative group, is a group in which the result of applying the group operation to two group elements does not depend on the order in which they are written. That is, the group operation is commut ...

under pointwise multiplication. This group is referred to as the

character group In mathematics, a character group is the group of representations of a group by complex-valued functions. These functions can be thought of as one-dimensional matrix representations and so are special cases of the group characters that arise in t ...

of ''G''. Sometimes only ''unitary'' characters are considered (characters whose

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...

is in the

unit circle In mathematics, a unit circle is a circle of unit radius—that is, a radius of 1. Frequently, especially in trigonometry, the unit circle is the circle of radius 1 centered at the origin (0, 0) in the Cartesian coordinate system in the Eucl ...

); other such homomorphisms are then called ''quasi-characters''. Dirichlet characters can be seen as a special case of this definition. Multiplicative characters are linearly independent, i.e. if

\chi_1, \chi_2, \ldots, \chi_n

are different characters on a group ''G'' then from

a_1\chi_1 + a_2\chi_2 + \cdots + a_n\chi_n = 0

it follows that

a_1 = a_2 = \cdots = a_n = 0.

Examples

*Consider the (''ax'' + ''b'')-group ::

G := \left\.

: Functions ''f''_''u'' : ''G'' → C such that

f_u \left(\begin
a & b \\
0 & 1  \end\right)=a^u,

where ''u'' ranges over complex numbers C are multiplicative characters. * Consider the multiplicative group of positive

real numbers In mathematics, a real number is a number that can be used to measure a ''continuous'' one-dimensional quantity such as a distance, duration or temperature. Here, ''continuous'' means that values can have arbitrarily small variations. Every real ...

(R⁺,·). Then functions ''f''_''u'' : (R⁺,·) → C such that ''f''_''u''(''a'') = ''a''^''u'', where ''a'' is an element of (R⁺, ·) and ''u'' ranges over complex numbers C, are multiplicative characters.

References

* Lectures Delivered at the University of Notre Dame Group theory {{group-theory-stub