算法設計漸進符号

1．θ漸進确界：存在正常量c1,c2.n0,對于所有n>n0,有0<=c1g(n)<=f(n)<=c2g(n)。

2.Ο漸進上界：當隻有漸進上界時存在正常量c和n0，使得對所有n>=n0,0<=f(n)<=cg(n)。

3.Ω漸進下界：當隻有漸進下界時存在正常量c和n0，使得對所有n>=n0,0<=cg(n)<=f(n)。

4.ο非漸進緊确上界：對于任意正常量c,存在常數n0>0，對所有n>n0,0<f(n)<cg(n)。O記号所提供的漸進上界可能不是漸進緊确的界。我們使用“o”，來表示非漸進緊确的上界。

如：2n2=O(n2),2n=o(n2)

5.ω非漸進緊确下界：對于任意正常量c,存在常數n0>0，對所有n>n0,0<cg(n)<f(n)。

如：n2=ω(n),

成語學習：

狡兔死，良狗亨；高鳥盡，良弓藏；敵國破，謀臣亡。

出自韓信，顯示于劉邦與韓信，趙構與嶽飛，朱元璋與常遇春，趙匡胤與石守信，勾踐與文重等。

名言：沒有不可治愈的傷痛，沒有不能結束的沉淪，所有失去的，都會以另一種方式歸來。–約翰·肖爾斯

某事尚不确定：there is considerable uncertainty about something

a big question-mark hangs over something

轉折句型：At first glance…,A closer look,however,suggests…

大不如前：something is worse off

be a shadow its former self

eg:A decade ago Nokia was the undisputed leader in the global mobile industry,but now it is just a shadow of its former self. its decline was mainly attributed to corporate bureaucracy and short-sightedness.

很難做…而不…：It is hard to… without…

eg: It is hard to talk about Chinese science fiction these days without mentioning Liu Cixin,the author of The Wandering Earth,which has recently been adapted for cinema.