Why is rand faster than rand(1) ?

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sunil anandatheertha 2020-7-21

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https://ww2.mathworks.cn/matlabcentral/answers/568455-why-is-rand-faster-than-rand-1

评论： sunil anandatheertha 2020-7-22

I am optimizing my monte-carlo codes and have a question on rand function. Below, i give simple codes to get a random number. All three of the below works for my problem. Looking at the elapsed times, I want to know why is rand faster than rand(1)? Although I kind of know why method 3 is fast, your comments are most welcome.

%%%%%%%%%%%%%%
% METHOD - 1
tic
for count = 1:1e7
    a = rand;
end
toc
% Elapsed time is 0.383401 seconds.
%%%%%%%%%%%%%%
% METHOD - 2
tic
for count = 1:1e7
    a = rand(1);
end
toc
% Elapsed time is 7.589860 seconds.
%%%%%%%%%%%%%%
% METHOD - 3
a = rand(1e7,1);
tic
for count = 1:numel(a)
    aa = a(count);
end
toc
% Elapsed time is 0.139859 seconds.
%%%%%%%%%%%%%%