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In mathematics, the linear algebra concept of dual basis can be applied in the context of a finite extension ''L''/''K'', by using the field trace. This requires the property that the field trace ''Tr''''L''/''K'' provides a non-degenerate quadratic form over ''K''. This can be guaranteed if the extension is separable; it is automatically true if ''K'' is a perfect field, and hence in the cases where ''K'' is finite, or of characteristic zero. A dual basis is not a concrete basis like the polynomial basis or the normal basis; rather it provides a way of using a second basis for computations. Consider two bases for elements in a finite field, GF(''p''''m''): : then ''B''2 can be considered a dual basis of ''B''1 provided : Here the trace of a value in GF(''p''''m'') can be calculated as follows: : Using a dual basis can provide a way to easily communicate between devices that use different bases, rather than having to explicitly convert between bases using the change of bases formula. Furthermore, if a dual basis is implemented then conversion from an element in the original basis to the dual basis can be accomplished with a multiplication by the multiplicative identity (usually 1). 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「Dual basis in a field extension」の詳細全文を読む スポンサード リンク
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