How to speed up my code and improve/avoid for loop

2017 10 12
1 个回答
更新时间：2017 10 12
4 次查看（30 天）

0 个投票

Dear all, that's my piece of code that works correctly but too slow.
T=rand(100000,1)-0.3;
eTG=zeros(size(T)); %set eTG(1)=0 and preallocate
for i=2:length(T)
eTG(i)=eTG(i-1)+T(i-1);
eTG(i(eTG(i)>0))=0;
end
Preallocation doesn't help and "run and time" tool shows that string
eTG(i(eTG(i)>0))=0;
eats 83% of the total time. Please give me your advices how to optimize this code. Are there any ways to vectorize this code and avoid loops at all?

5 个评论
显示 3更早的评论 隐藏 3更早的评论

per isakson
per isakson 2017-10-12
Given i is a scalar, what is
eTG(i(eTG(i)>0))=0
supposed to do?
Sergei Zhuravlev
Sergei Zhuravlev 2017-10-12
编辑：Sergei Zhuravlev 2017-10-12
Check if eTG variable is positive on every step and if yes, sets it to zero
Walter Roberson
Walter Roberson 2017-10-12
Replace that with
eTG(i) = max(0, eTG(i));
Could you confirm that you want negative values to be left untouched, but positive values to be set to 0?
Sergei Zhuravlev
Sergei Zhuravlev 2017-10-12
编辑：Sergei Zhuravlev 2017-10-12
Yes, exactly. Using max function gives wrong results, Should be "min" I suppose. Thank you!
Walter Roberson
Walter Roberson 2017-10-12
Dang, I got it wrong this time too. Yes, min(0, eTG(i)) if you want negative untouched and positive set to 0.

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回答（1 个）

Sergei Zhuravlev
Sergei Zhuravlev 2017-10-12
编辑：Sergei Zhuravlev 2017-10-12

0 个投票

This code is 10 times faster (thanks to Walter Roberson)
T=rand(100000,1)-0.3;
eTG=zeros(size(T)); %set eTG(1)=0 and preallocate
for i=2:length(T)
eTG(i)=eTG(i-1)+T(i-1);
eTG(i) = min(0, eTG(i));
end

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