[問題] C的兩種寫法結果不同?
如題~~
目前我有一個程式需更改~所以我用了另一個寫法~
但我兩種寫法明明就是在講一樣的東西~
但我跑兩者的performance(跑很多個loop平均算他的錯誤率)就是會不一樣~
(由於我跑錯誤率需要跑超多loop~所以我debug僅能printf幾次來看這兩種寫法是否相同~
兩種寫法printf出來的東西是一樣的)
<寫法1>
for(i=2;i<N;i++)
{
if(i==2)
{
delta_a[i]=delta_Tx1*Rtilde_Real[i][i];
}
else
{
delta_a[i]=delta_a[i-1]*Rtilde_Rea[i-1][i-1]*Rtilde_Real[i][i];
}
}
<寫法2>
delta_a[2]=delta_Tx1*Rtilde_Real[2][2];
delta_a[3]=delta_a[2]*Rtilde_Real[2][2]*Rtilde_Real[3][3];
兩者好像是講一樣的東西~
但跑很多loop來算performance就是會不一樣~
我很確定我程式中的差異就在這兩種的差別而已~
不知道是C內部有無特殊的規定還是我犯的問題其實很蠢~
若這問題有點笨~還請版上高人指點我~
若回答有點長~歡迎站內信指點迷津Orz
附上程式碼 : http://codepad.org/DkFsuCkd
其於部分不用管他~差別僅在於<寫法1>和<寫法2>跑出來結果不同而已~
--
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