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单词 Contraction
释义

contraction


Definition Let ω be a smooth k-form on a smooth manifoldMathworldPlanetmath M,and let ξ be a smooth vector field on M. The contractionof ω with ξ is the smooth (k-1)-form that maps xM toωx(ξx,).In other words, ω ispoint-wise evaluated with ξ in the first slot.We shall denote this (k-1)-form by ιξω.If ω is a 0-form, we set ιξω=0 for all ξ.

Properties Let ω and ξ be as above. Thenthe following properties hold:

  1. 1.

    For any real number k

    ιkξω=kιξω.
  2. 2.

    For vector fields ξ and η

    ιξ+ηω=ιξω+ιηω,
    ιξιηω=-ιηιξω,
    ιξιξω=0.
  3. 3.

    Contraction is an anti-derivation [1]. Ifω1 is a p-form, and ω2 is a q-form, then

    ιξ(ω1ω2)=(ιξω1)ω2+(-1)pω1(ιξω2).

References

  • 1 T. Frankel,Geometry of physics,Cambridge University press,1997.
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更新时间:2025/5/4 12:50:03