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

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?

[per isakson]

Given i is a scalar, what is

eTG(i(eTG(i)>0))=0

supposed to do?

[Sergei Zhuravlev]

Check if eTG variable is positive on every step and if yes, sets it to zero

[Walter Roberson]

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]

Yes, exactly. Using max function gives wrong results, Should be "min" I suppose. Thank you!

[Walter Roberson]

Dang, I got it wrong this time too. Yes, min(0, eTG(i)) if you want negative untouched and positive set to 0.

Answer 1

[Sergei Zhuravlev]

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