removing three loops which are predeterminded

som
2012 3 31
2 个回答
回答已采纳
2 次查看（30 天）

0 个投票

Hi all
I've writen a program including four loops and they all located inside a "while" loop as below:
q=[0,10,20; 40,50,60; 10,20,30;] ;
s=[0;10;20;30];
r=[10;20;30;40];
nq=size(q,2);
ns=length(s);
nr=length(r);
n=1;
while n<10000
for t=3:-1:1
for ss=1:ns
for qq=1:nq
for rr=1:nr
s2{t,ss}(qq,rr)= s(ss)+q(t,qq)-r(rr);
if s2{t,ss}(qq,rr)<=100 && s2{t,ss}(qq,rr)>=0
tsd{t,ss}(qq,rr)=10^25;
else
s2{t,ss}(qq,rr)=-1e6;tsd{t,ss}(qq,rr)=-1e25;
end
end
end
end
n=n+1;
end
end
since the values of "ss", " qq" and "rr" are predeterminded, I want to vectorize above programand and finally decrease the number of loops by removing "ss","qq" and "rr" loops, respectively.
How can I remove three mentioned loops in the way all results related to "s2" and "tsd" be visible sepratly. any help would be appreciated.

10 个评论
显示 8更早的评论 隐藏 8更早的评论

Walter Roberson
Walter Roberson 2012-3-31
http://www.mathworks.com/matlabcentral/answers/29922-why-your-question-is-not-urgent-or-an-emergency
Walter Roberson
Walter Roberson 2012-3-31
What is the difference between this question and your previous and still active question http://www.mathworks.com/matlabcentral/answers/33965-removing-three-loops-which-are-predeterminded
Jan
Jan 2012-3-31
@somayeh: The term "urgent" discourage others from answering.
Walter Roberson
Walter Roberson 2012-3-31
Yup. For example I'm going to have a shower instead of thinking about it.
Jan
Jan 2012-3-31
Dear Walter, I personally appreciate your brain. I do not hesitate to assume, that it can solve such problems even during having your shower. But a really urgent question would encourage you to even type in the answer from inside your shower stall.
som
som 2012-3-31
Dear friends, if I wrote "urgent question", I meant that my question is essential to be answered as soon as possible, not any more.
any way, thanks for your comments.
Jan
Jan 2012-3-31
Please do not take the discussion about "urgent" personally. You participated in this forum for 285 day now, asked a lot of questions, know how to format code and how to accept an answer. Then one can assume, that you have seen the 2nd most voted thread (see Walter's 1st comment) already.
I believe you, that a fast answer is essential for you. At the same time I'm convinced, that this is not essential for any of the voluntary contributors of this forum, because they (we) spend their spare time here. Therefore any kind of "as soon as possible" does not really match.
Do *you* create answers faster, if the question contains an "urgent"?!
However, you have edited your question. Beside remove the discussed term, you have removed your partially vectorized version. Why? Does my answer loose its meaning also, such that I should delete it?
som
som 2012-3-31
I personally create answers faster, if the question contains an "urgent".
about other questions:
I tought the second part of above program i.e. my answer made the program a bit confusing. So, I prefer to remove it. But you got the meaning completely right ane your answer is still true.
Walter Roberson
Walter Roberson 2012-3-31
som, if you create answers faster if the question contains an "urgent", then that must be on some other forum, as you have not answered any questions at all here.
Jan
Jan 2012-4-1
@Walter: "Faster" can be related to an event in the future also.

请先登录，再进行评论。

请先登录，再回答此问题。

 采纳的回答

Jan
Jan 2012-3-31

0 个投票

I do not see a method to avoid all loops. And even if this is possible, it is not guaranteed to be more efficient.
Anyhow, you can improve the current version:
s2 = cell(3, ns); % Pre-allocate!
tsd = cell(3, ns);
while n<10000
for t = 3:-1:1
a = bsxfun(@minus, q(t, :)', r);
for ss = 1:ns
b = s(ss) + a;
index_out = b > 100 | b < 0;
% index_in is not needed!
% index_in = s2{t,ss} <= 100 & s2{t,ss} >= 0;
% But if it is needed: index_in = not(index_out);
b(index_out) = -1e6;
s2{t, ss} = b;
tsd{t, ss}(index_out) = -1e25;
end
n = n+1;
end
end

2 个评论
显示 无 隐藏 无

som
som 2012-3-31
thanks.In your idea there is no solution for removing all three loops containing "ss", " qq" and "rr" loops?
thanks
Jan
Jan 2012-4-1
No, I did not try to remove all loops, because I do not assume, that this will be an improvement. In general the removing of a loop requires the creation of an temporary array. The larger the temporary arrays, the smaller is the benefit of vectorizing. With pre-allocation a FOR-loop can be the fastest method.

请先登录，再进行评论。

更多回答（1 个）

som
som 2012-4-3

0 个投票

Dear Jan Simon,
since writing of above program by keeping just one loop i.e. " t loop" is so essential for me and on the other hand it's a main part of my project, could you please try for it and give me your valuable feedback. thanks

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Jan
Jan 2012-4-3
Dear som, I'm convinced that a fully vectorized method is slower than the shown code, especially if you store the data in form of cells in s2 and tsd. I cannot understand, why you want to avoid the loop and in consequence I cannot guess the requirements of the new code.
There is still a potential for further accelerations in the code. E.g.:
b = s(ss) + a;
index_out = b > 100 | b < 0;
can be expressed as:
index_out = abs(s(ss) + a - 50) > 50;
However, without knowing what you actually want to achieve, further suggestions are guesswork only.

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by