Modular Function Article Index for
Modular
Website Links For
Modular
 

Information About

Modular Function




In Mathematics , modular functions are certain kinds of Mathematical Function s mapping Complex Number s to complex numbers. There are a number of other uses of the term "modular function" as well; see below for details.

Formally, a function ''f'' is called modular or a '''modular function''' Iff it satisfies the following properties:

# ''f'' is Meromorphic in the open Upper Half-plane ''H''.
# For every Matrix ''M'' in the Modular Group Γ , ''f''(''M''τ) = ''f''(τ).
# The Laurent Series of ''f'' has the form

::f( au) = \sum_{n=-m}^\infty a(n) e^{2i\pi n au}.

It can be shown that every modular function can be expressed as a Rational Function of Klein's Absolute Invariant ''j''(τ), and that every rational function of ''j''(τ) is a modular function; furthermore, all Analytic modular functions are Modular Form s, although the converse does not hold. If a modular function ''f'' is not identically 0, then it can be shown that the number of zeroes of ''f'' is equal to the number of Pole s of ''f'' in the Closure of the Fundamental Region ''R''Γ.


OTHER USES


There are a number of other usages of the term ''modular function'', apart from this classical one; for example, in the theory of Haar Measure s, it is a function Δ(''g'') determined by the conjugation action.


REFERENCES

  • Tom M. Apostol, ''Modular functions and Dirichlet Series in Number Theory'' (1990), Springer-Verlag, New York. ISBN 0-387-97127-0

  • Robert A. Rankin, ''Modular forms and functions'', (1977) Cambridge University Press, Cambridge. ISBN 0-521-21212-X