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The term external is useful for describing certain algebraic structures. The term comes from the concept of an external binary operation which is a binary operation that draws from some ''external set''. To be more specific, a left external binary operation on ''S'' over ''R'' is a function and a right external binary operation on ''S'' over ''R'' is a function where ''S'' is the set the operation is defined on, and ''R'' is the external set (the set the operation is defined ''over''). == Generalizations == The ''external'' concept is a generalization rather than a specialization, and as such, it is different from many terms in mathematics. A similar but opposite concept is that of an ''internal binary function'' from ''R'' to ''S'', defined as a function . Internal binary functions are like binary functions, but are a form of specialization, so they only accept a subset of the domains of binary functions. Here we list these terms with the function signatures they imply, along with some examples: * (binary function) * * Example: exponentiation ( as in ), * * Example: set membership ( where is the category of sets) * * Examples: matrix multiplication, the tensor product, and the Cartesian product * (internal binary function) * * Example: internal binary relations () * * Examples: the dot product, the inner product, and metrics. * (external binary operation) * * Examples: dynamical system flows, group actions, projection maps, and scalar multiplication. * (binary operation). * * Examples: addition, multiplication, permutations, and the cross product. 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「External (mathematics)」の詳細全文を読む スポンサード リンク
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