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

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Sergei Zhuravlev 2017-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/360923-how-to-speed-up-my-code-and-improve-avoid-for-loop

编辑： Sergei Zhuravlev 2017-10-12

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?

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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 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 2017-10-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/360923-how-to-speed-up-my-code-and-improve-avoid-for-loop#answer_285415

编辑：Sergei Zhuravlev 2017-10-12

在 MATLAB Online 中打开

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