In mathematics, the term mapping, sometimes shortened to map, is a relationship between mathematical objects or structures.
Maps may either be functions or morphisms, though the terms share some overlap. In the sense of a function, a map is often associated with some sort of structure, particularly a set constituting the codomain. Alternatively, a map may be described by a morphism in category theory, which generalizes the idea of a function. There are also a few, less common uses in logic and graph theory.
Maps as functionsEdit
In many branches of mathematics, the term map is used to mean a function, sometimes with a specific property of particular importance to that branch. For instance, a "map" is a continuous function in topology, a linear transformation in linear algebra, etc.
Some authors, such as Serge Lang, use "function" only to refer to maps in which the codomain is a set of numbers (i.e. a subset of the fields R or C) and the term mapping for more general functions.
A partial map is a partial function, and a total map is a total function. Related terms like domain, codomain, injective, continuous, etc. can be applied equally to maps and functions, with the same meaning. All these usages can be applied to "maps" as general functions or as functions with special properties.
Maps as morphismsEdit
In category theory, "map" is often used as a synonym for morphism or arrow, thus for something more general than a function. For example, morphisms , in a concrete category, in other words morphisms that can be viewed as functions, carry with them the information of both its domain (the source of the morphism), but also its co-domain (the target ). In the widely used definition of function , this is a subset of consisting of all the pairs for . In this sense, the function doesn't capture the information of which set is used as the co-domain. Only the range is determined by the function.
In graph theoryEdit
In computer scienceEdit
In the communities surrounding programming languages that treat functions as first-class citizens, a map often refers to the binary higher-order function that takes a function f and a list [v0, v1, ..., vn] as arguments and returns [f(v0), f(v1), ..., f(vn)], where n ≥ 0.
- The words map, mapping, transformation, correspondence, and operator are often used synonymously. Halmos 1970, p. 30. In many authors, the term 'map' is with a more general meaning than 'function', which may be restricted to having domains of sets of numbers only.
- T. M. Apostol (1981). Mathematical Analysis. Addison-Wesley. p. 35.
- Lang, Serge (1971), Linear Algebra (2nd ed.), Addison-Wesley, p. 83
- Simmons, H. (2011), An Introduction to Category Theory, Cambridge University Press, p. 2, ISBN 9781139503327
- Gross, Jonathan; Yellen, Jay (1998), Graph Theory and its applications, CRC Press, p. 294, ISBN 0-8493-3982-0