MATLAB: Choosing from numbers whose sum is X

computefixedrandomsamplesum

hi all,

suppose i generate 1000 random numbers and want to pick five out of that 1000 so that the sum of the five numbers is 100. if there is no way so the sum equal to 100 then i will just re run it. it doesnt have to work always…thank you!!

Best Answer

I suppose you mean integers, but you don't say....

N = round(randn(1,1000));
S = 0;
maxiter = 2e6;
cnt = 1;
while S~=5 & cnt<maxiter
   R = ceil(rand(1,5)*1000);
   S = sum(N(R));
   cnt = cnt + 1;
end

Now we have the numbers, so look at them:

nums = N(R)
sum(nums)

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MATLAB: How to Generate random number that most of them ZEROs

x=zeros(1,50);
r=rand(1,50);
PrZero = .8;  % Adjust as needed to achieve "most of them zeros"
x(r<(1-PrZero)/2) = 1;
x(r>1-(1-PrZero)/2) = 2;
histogram(x);

MATLAB: Randomly dividing an integer (non-uniform distribution)

There are any number of ways to do that, depending on exactly what you mean by "considerably". Here are a few:

%% Transform the numbers so they aren't uniform to begin with.
M=20;
N = 1;
n = rand(1,M).^10;  % Increase the exponent to increase the size variation.  A lot of numbers will be near zero.
TOT = sum(n);
numbers = (n/TOT)*N
%%  Generate progressively smaller numbers by generating each new one as a uniform(0,1) fraction of
% what is left of your total.
M=20;
n = rand(1,M);
TOT = sum(n);
cumtot = cumsum(n(1:end-1));
n(1:end-1) = n(1:end-1) .* (TOT - cumtot);
TOT = sum(n);
numbers = (n/TOT)*N
% permute(numbers) here if you don't want larger numbers to be systematically first.

Best Answer

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MATLAB: How to Generate random number that most of them ZEROs

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