Dirichlet function

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In mathematics, the Dirichlet function [1] [2] is the indicator function of the set of rational numbers over the set of real numbers , i.e. for a real number x if x is a rational number and if x is not a rational number (i.e. is an irrational number).

Contents

It is named after the mathematician Peter Gustav Lejeune Dirichlet. [3] It is an example of a pathological function which provides counterexamples to many situations.

Topological properties

Periodicity

For any real number x and any positive rational number T, . The Dirichlet function is therefore an example of a real periodic function which is not constant but whose set of periods, the set of rational numbers, is a dense subset of .

Integration properties

See also

References

  1. "Dirichlet-function", Encyclopedia of Mathematics , EMS Press, 2001 [1994]
  2. Dirichlet Function — from MathWorld
  3. Lejeune Dirichlet, Peter Gustav (1829). "Sur la convergence des séries trigonométriques qui servent à représenter une fonction arbitraire entre des limites données". Journal für die reine und angewandte Mathematik. 4: 157–169. The function is defined on page 169
  4. Dunham, William (2005). The Calculus Gallery. Princeton University Press. p. 197. ISBN   0-691-09565-5.