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The concept of angles between lines in the plane and between pairs of two lines, two planes or a line and a plane in space can be generalised to arbitrary dimension. This generalisation was first discussed by Jordan.〔 For any pair of flats in a Euclidean space of arbitrary dimension one can define a set of mutual angles which are invariant under isometric transformation of the Euclidean space. If the flats do not intersect, their shortest distance is one more invariant.〔 These angles are called canonical〔 or principal.〔 The concept of angles can be generalised to pairs of flats in a finite-dimensional inner product space over the complex numbers. ==Jordan's definition〔== Let and be flats of dimensions and in the -dimensional Euclidean space . By definition, a translation of or does not alter their mutual angles. If and do not intersect, they will do so upon any translation of which maps some point in to some point in . It can therefore be assumed without loss of generality that and intersect. Jordan shows that Cartesian coordinates in can then be defined such that and are described, respectively, by the sets of equations : : : and : : : with . Jordan calls these coordinates canonical. By definition, the angles are the angles between and . The non-negative integers are constrained by : : : For these equations to determine the five non-negative integers completely, besides the dimensions and and the number of angles , the non-negative integer must be given. This is the number of coordinates , whose corresponding axes are those lying entirely within both and . The integer is thus the dimension of . The set of angles may be supplemented with angles to indicate that has that dimension. Jordan's proof applies essentially unaltered when is replaced with the -dimensional inner product space over the complex numbers. (For angles between subspaces, the generalisation to is discussed by Galántai and Hegedũs in terms of the below variational characterisation.〔) 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「Angles between flats」の詳細全文を読む スポンサード リンク
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