放屁
Identity Matrix -- from Wolfram MathWorld 美麗的某小姐有一個不太好的習慣,就是喜歡放屁。 一天,這位小姐要搭公車上班, 身邊照例有數位熱情的追求者尾隨在她後面, 上了車沒多久,小姐的老毛病就忍不住犯了, 身邊一位男士很機警馬上大聲說"是我放的" 可是沒過多久,小姐The identity matrix is a the simplest nontrivial diagonal matrix, defined such that I(X)=X (1) for all vectors X. An identity matrix may be denoted 1, I, or E (the latter being an abbreviation for the German term "Einheitsmatrix"; Courant and Hilbert 1989...
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