create array

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Mate 2u
Mate 2u 2011-5-9
Hi considering I want to make a a 3x6624 matrix of random numbers (>0 and <1) but I want the sum of each column of the3 numbers to add up to 1. Any help?
Thanks

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采纳的回答

Paulo Silva
Paulo Silva 2011-5-9
a=zeros(3,6624);
for b=1:size(a,2)
c(1)=rand/3;
c(2)=rand/3;
c(3)=1-c(1)-c(2);
cr=randperm(3);
a(:,b)=[c(cr(1));c(cr(2));c(cr(3))];
end
  1 个评论
Mate 2u
Mate 2u 2011-5-9
Is there anyway to do it faster without a loop?

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更多回答（3 个）

Mate 2u
Mate 2u 2011-5-9
Is there a way to do this without a loop? So it could perform faster?
Sean de Wolski
Sean de Wolski 2011-5-9
A = rand(3,6624);
A = bsxfun(@rdivide,A,sum(A,1));
Also look at Roger's randfixedsum on the FEX.
Teja Muppirala
Teja Muppirala 2011-5-9
Paulo's algorithm without a loop:
a=zeros(3,6624);
a(1:2,:)=rand(2,6624)/3;
a(3,:)=1-sum(a);
P = randperm(6624*3);
[~,ord] = sort(ceil(P/3));
a(:) = a(P(ord));
figure
hist(a',.05:.1:.95);
Another possible algorithm:
a=zeros(3,6624);
a(1,:) = rand(1,6624);
a(2,:) = (1-sum(a)).*rand(1,6624);
a(3,:) = (1-sum(a)).*rand(1,6624);
a = bsxfun(@rdivide,a,sum(a));
P = randperm(6624*3);
[~,ord] = sort(ceil(P/3));
a(:) = a(P(ord));
figure
hist(a',.05:.1:.95);

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