Need to speed up the generation of random numbers.

Question

Eleftherios Oikonomopoulos 2021-5-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/832438-need-to-speed-up-the-generation-of-random-numbers

回答： DGM 2021-5-17

Hi to all,

I have a 4-D array A of size 81x81x120x120. Each element of this array is an integer with values between 0 and 5.

Now for each element of this array, I need to generate as many random numbers as the value of the element.

For example, if A(1, 1, 1, 1) = 5, I must generate 5 random numbers.

I have tried this approach with the arrayfun:

C = arrayfun(@(x) rand(x, 1), A, 'UniformOutput', false);

where the output is a cell array of the same size as A and each cell contains as many random numbers as the integer value of the corresponding element of A.

Now this approach works, but it's too slow for the purposes of my problem, since I need to run this 500 times.

Is there any way to speed it up?

Thank you very much!

Best,

Eleftherios

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

James Tursa 2021-5-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/832438-need-to-speed-up-the-generation-of-random-numbers#answer_701848

编辑：James Tursa 2021-5-17

You could over generate a large matrix and then pick off the number of elements you need later. E.g.,

C = rand([5 size(A)]);

Then e.g. for the (1,1,1,1) spot:

n = A(1,1,1,1);
r = C(1:n,1,1,1,1);

In general for the i,j,k,m spot:

n = A(i,j,k,m);
r = C(1:n,i,j,k,m);

etc.

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。

Answer 2

DGM 2021-5-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/832438-need-to-speed-up-the-generation-of-random-numbers#answer_701883

At least in my tests, this is somewhat faster:

n = 10;
A = randi(5,n,n,n); % generate test array
rv = rand(sum(A(:)),1); % generate all random numbers
C = reshape(mat2cell(rv,A(:),1),size(A)); % form a cell array out of them