User:Wttwcl/sandbox
對給定黎曼度量的二階張量的跡(trace)
已知若是-張量,則其跡(trace)為。
對二階張量我們定義其對應黎曼度量的跡(trace)為:
- ,
是-張量,所以其跡是有定義的。
設,為 -張量場,將第二指數上升讓-張量變成-張量即,
- 。
我們有
- 。
注意:雖然這裡是上升第二指數(raising the second index),不過對第一指數上升也會得到相同結果。
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已知若是-張量,則其跡(trace)為。
對二階張量我們定義其對應黎曼度量的跡(trace)為:
是-張量,所以其跡是有定義的。
設,為 -張量場,將第二指數上升讓-張量變成-張量即,
我們有
注意:雖然這裡是上升第二指數(raising the second index),不過對第一指數上升也會得到相同結果。