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co- +‎ domain



codomain (plural codomains)

  1. (mathematics, analysis) The target set into which a function is formally defined to map elements of its domain; the set denoted Y in the notation f : XY.
    • 1994, Richard A. Holmgren, A First Course in Discrete Dynamical Systems, Springer, page 11,
      Definition 2.5. A function is onto if each element of the codomain has at least one element of the domain assigned to it. In other words, a function is onto if the range equals the codomain.
    • 2006, Robert L. Causey, Logic, Sets, and Recursion, 2nd Edition, Jones & Bartlett Learning, page 192,
      Once we have described   as a function from   to  , by convention we will call   the codomain, even though other sets, of which   is a subset, could have been used. [] If   is an element of the codomain, then   iff there is some   in the domain such that   maps   to  .
    • 2017, Alan Garfinkel, Jane Shevtsov, Yina Guo, Modeling Life: The Mathematics of Biological Systems, Springer, page 12,
      For example, the codomain of   consists of all real numbers. A function links each element in its domain to some element in its codomain. Each domain element is linked to exactly one codomain element.

Usage notesEdit

The codomain always contains the image of the function (the actual set of points to which points of the domain are mapped), and can be larger if the function is not surjective.

The term range is often synonymous with codomain, but can also be used as a synonym for image.


  • (target set of a function): range


  • (target set of a function): domain


Further readingEdit