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In mathematics, an identity function, also called an identity relation or identity map or identity transformation, is a function that always returns the same value that was used as its argument. In equations, the function is given by . ==Definition== Formally, if ''M'' is a set, the identity function ''f'' on ''M'' is defined to be that function with domain and codomain ''M'' which satisfies :''f''(''x'') = ''x'' for all elements ''x'' in ''M''. In other words, the function assigns to each element ''x'' of ''M'' the element ''x'' of ''M''. The identity function ''f'' on ''M'' is often denoted by id''M''. In set theory, where a function is defined as a particular kind of binary relation, the identity function is given by the identity relation, or ''diagonal'' of ''M''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Identity function」の詳細全文を読む スポンサード リンク
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