How to vectorize this for loop

Question

Leo Tu 2021-7-5

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/872158-how-to-vectorize-this-for-loop

评论： Leo Tu 2021-7-5

matlab.mat

I have the following script which I have managed to test for up to t=200 however I need it to go up to t=12054 and it takes too long to run.

Could anyone please help with vectorizing the code so that it can run faster? I have attached my data T

% T is a column of temperature data over 12054 days
V = flip(T,1) 
syms k; 
for t=1:12054 
L(t) = 1+symsum(.5.^(abs(k-5)*V(t)),k,0,12054-t)/symsum(.5.^abs(k-5),k,0,12054-t); 
end 
lambda = double(L); 
lambda = flip(lambda,2)  % flipping back because we initially flipped T to get V. 
r = poissrnd(lambda); 
plot(r) 

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Paul 2021-7-5

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/872158-how-to-vectorize-this-for-loop#answer_740268

编辑：Paul 2021-7-5

在 MATLAB Online 中打开

For starters, why use symsum at all? Doesn't sum() do exactly what is needed?

for t = 1:12054
    k = 0:(12054 - t);
    L(t) = 1 + sum(0.5.^(abs(k-5).*V(t)))./sum(0.5.^(abs(k-5)));
end
lambda = flip(L,2);

I suspect other optimizations can be made as well. For sure, pre-allocate L. But for only 12054 elements, this loop may be fast enough for what's needed.