Optimization of code with double for-loops

Question

Howard Wilton 2022-11-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1857003-optimization-of-code-with-double-for-loops

评论： Howard Wilton 2022-11-20

I am looking to optimize the following code specifically, and more generally, I am trying to learn optimization techniques in MATLAB for a larger project. The code below is just a snippet example which I am looking to learn techniques and then apply to a larger problem. I am potentially looking at values of L being as high as

with four nested loops as opposed to just the two shown below.

Any pointers (or links to decent YouTube video on MATLAB optimization) would be welcomed.

clc; clearvars;
T = 1; Ts = 1e-2; t = 0:Ts:L*T;
L = 2^5; 
start_time = clock(); 
for l = 0:L-1
    for q = 0:L-1
        flag = (t>=(l-q-1)*T) & (t<=(l-q+1)*T);
        partA = (T-abs(t-(l-q)*T));
    end
end
elapsed_time = clock();
time = elapsed_time(4)*3600+elapsed_time(5)*60+elapsed_time(6)

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Howard Wilton 2022-11-20

The questions didn't really hit the answer so i thought i would cast the questions differently.

However, your advice is duly noted and i shall be careful in the future. Thanks.

Howard Wilton 2022-11-20

编辑：Howard Wilton 2022-11-20

I have taken the code a bit further and managed to dispense with the nested loops . However, I still need a 1D loop. Performance is substantially improved.

clc; clearvars;

L = 2^8; T = 1; t = 0:0.2:L*T;

start_time = clock();

l = 1:L; q = 1:L;

X = (l(:)-q(:).')*T;

for loop = 1:length(t)

t2(:,:,loop) = t(loop) - X;

end

stop_time = elapsedTime(start_time)

function time = elapsedTime(start_time)

elapsed_time = clock-start_time;

time = elapsed_time(4)*3600+elapsed_time(5)*60+elapsed_time(6);

end

Keen to figure out a way to eliminate the 1D loop and generate a

matrix

.

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Answer 1

Walter Roberson 2022-11-20

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https://ww2.mathworks.cn/matlabcentral/answers/1857003-optimization-of-code-with-double-for-loops#answer_1105788

在 MATLAB Online 中打开

X = (l(:)-q(:).')*T;
for loop = 1:length(t)
  t2(:,:,loop) = t(loop) - X;
end

replace with

t2 = reshape(t, 1, 1, []) - X;

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Howard Wilton 2022-11-20

thankyou !!

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