Optimization of code with double for-loops
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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.
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)
4 个评论
Walter Roberson
2022-11-20
for q = 0:L-1
flag = (t>=(l-q-1)*T) & (t<=(l-q+1)*T);
Catalytic
2022-11-20
@Howard Wilton You appear to have opened several previous threads on similar subjects to this and abandoned them, without accepting an answer or follow-up discussion. It is better if you not do this, so that contributors can know if the question is to be taken seriously.
Howard Wilton
2022-11-20
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 
.
matrix . 采纳的回答
Walter Roberson
2022-11-20
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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