推 genius945:跟多重那邊的speed up 有點像@@" 11/28 23:08
→ genius945:wh大好強阿....可否請問你的進度參考... 11/28 23:13
推 mqazz1:wh大真的很強 11/29 00:12
→ wheels:我覺得B大更強，我只是盡力回答而已O_O 11/29 00:14
→ wheels:進度的話大概是第二次的一半吧，囧。 11/29 00:19
推 kiwidoit:好厲害!! 11/29 04:18
※ 引述《seacottobaby (海綿寶寶)》之銘言：
: We make an enhancement to a computer that improves some mode of execution
: by a factor of 10. Enhanced mode is used 80% of the time,measured as a
: percentage of the execution time when the enhanced mode is in use.
: (1) What is the speedup we have obtained from fast mode?
: Ans : Speedup = Time(unenhanced) / Time(enhanced)
: The unenhanced time is the sum of the time that does not benefit from
: the 10 times faster speedup,plus the time that does benefit , but before
: its reduction by the factor of 10. Thus
: Time(unenhanced) = 0.2 X Time(enhanced) + 10 X 0.8 X Time(enhanced)
: = 8.2 Time(enhanced)
: 我不太了解解答的意思... 為什麼不是 speed = 1 / ( (0.8/10) + 0.2 ) 這樣?
因為題目有陷阱，
它給的80%是在enhanced mode底下的execution time之80%為加速的部分。
若令enhanced mode之execution time為x，
則0.2x為在enhanced mode下沒有被加速的部分，
這個部分會跟unenhanced mode所需花的時間一樣。
所以unenhanced mode總共的execution time為0.2x + 0.8x * 10
0.8x * 10 是為了把加速完的部分還原回來。
畫個圖就很清楚了
▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇▇▇▇▇ unenhanced execution time
^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
無法被加速 可被加速
(此區塊不變)
▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇ enhanced execution time = x
^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^
無法被加速 被加速完
0.2x 0.8x
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