choosing from numbers whose sum is X

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!!

Answer 1

[Matt Fig]

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)

[Matlabbey]

hi, thank you yes i do mean integers. but this doesnt seem to have a fixed sum?

[Matt Fig]

What do you mean, no fixed sum? I generated 100 random numbers and chose 5 whos sum is 5. If you need to change it to the sum being 100, then just use:

while S~=100

You might also like a different distribution. So:

N = round(randn(1,1000)*20);
N = randi(100,1,1000); % etc...

[Matlabbey]

sorry, you're right!! thank you!!

Answer 2

[Sean de Wolski]

FEX:randfixedsum