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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク torus knot ： ウィキペディア英語版 torus knot In knot theory, a torus knot is a special kind of knot that lies on the surface of an unknotted torus in R3. Similarly, a torus link is a link which lies on the surface of a torus in the same way. Each torus knot is specified by a pair of coprime integers ''p'' and ''q''. A torus link arises if ''p'' and ''q'' are not coprime (in which case the number of components is gcd(''p, q'')). A torus knot is trivial (equivalent to the unknot) if and only if either ''p'' or ''q'' is equal to 1 or −1. The simplest nontrivial example is the (2,3)-torus knot, also known as the trefoil knot. == Geometrical representation == A torus knot can be rendered geometrically in multiple ways which are topologically equivalent (see Properties below) but geometrically distinct. The convention used in this article and its figures is the following. The (''p'',''q'')-torus knot winds ''q'' times around a circle in the interior of the torus, and ''p'' times around its axis of rotational symmetry. If ''p'' and ''q'' are not relatively prime, then we have a torus link with more than one component. The direction in which the strands of the knot wrap around the torus is also subject to differing conventions. The most common is to have the strands form a right-handed screw for ''p q > 0''.〔Livingston, Charles (1993). ''Knot theory''. Mathematical Association of America. ISBN 0-88385-027-3〕〔Murasugi, Kunio (1996). ''Knot theory and its applications''. Birkhäuser. ISBN 3-7643-3817-2〕〔Kawauchi, Akio (1996). ''A survey of knot theory''. Birkhäuser. ISBN 3-7643-5124-1〕 The (''p'',''q'')-torus knot can be given by the parametrization :$\backslash begin$ x &= r\cos(p\phi) \\ y &= r\sin(p\phi) \\ z &= -\sin(q\phi) \end where $r\; =\; \backslash cos(q\backslash phi)+2$ and . This lies on the surface of the torus given by $(r-2)^2\; +\; z^2\; =\; 1$ (in cylindrical coordinates). Other parameterizations are also possible, because knots are defined up to continuous deformation. The illustrations for the (2,3)- and (3,8)-torus knots can be obtained by taking $r\; =\; \backslash cos(q\backslash phi)+4$, and in the case of the (2,3)-torus knot by furthermore subtracting respectively $3\backslash cos((p-q)\backslash phi)$ and $3\backslash sin((p-q)\backslash phi)$ from the above parameterizations of ''x'' and ''y''. The latter generalizes smoothly to any coprime ''p,q'' satisfying 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「torus knot」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.