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In many cases, such as order theory, the inverse of the indicator function may be defined. This is commonly called the generalized Möbius function, as a generalization of the inverse of the indicator function in elementary number theory, the Möbius function. (See paragraph below about the use of the inverse in classical recursion theory.)
Such indicators have some special properties. For example, the following statements are all true for an indicator function that is trigonometrically convex at least on an interval (,): [1]: 55–57 [2]: 54–61
Another use of the Iverson bracket is to simplify equations with special cases. For example, the formula (,) = = is valid for n > 1 but is off by 1 / 2 for n = 1.To get an identity valid for all positive integers n (i.e., all values for which () is defined), a correction term involving the Iverson bracket may be added: (,) = = (() + [=])
In mathematics, the Dirichlet function [1] [2] is the indicator function of the set of rational numbers, i.e. () = if x is a rational number and () = if x is not a rational number (i.e. is an irrational number).
Example [ edit ] If S is the set of natural numbers N {\displaystyle \mathbb {N} } , and T is some subset of the natural numbers, then the indicator vector is naturally a single point in the Cantor space : that is, an infinite sequence of 1's and 0's, indicating membership, or lack thereof, in T .
A simple function can be written in different ways as a linear combination of indicator functions, but the integral will be the same by the additivity of measures. Some care is needed when defining the integral of a real-valued simple function, to avoid the undefined expression ∞ − ∞ : one assumes that the representation
1 C (n), the indicator function of the set C ⊂ Z, for certain sets C. The indicator function 1 C (n) is multiplicative precisely when the set C has the following property for any coprime numbers a and b: the product ab is in C if and only if the numbers a and b are both themselves in C. This is the case if C is the set of squares, cubes, or k ...
The sinc function for a non-Cartesian lattice (e.g., hexagonal lattice) is a function whose Fourier transform is the indicator function of the Brillouin zone of that lattice. For example, the sinc function for the hexagonal lattice is a function whose Fourier transform is the indicator function of the unit hexagon in the frequency space. For a ...