how to generate a random array list with fixed sum ?

this code distributes fixed number in an array list, for exemple we have sum = 10, and the size of the array list is 3

the code generates this distribution [ 8 1 1] or other distribution...how can I modify this code to obtain a distribution that each value must be between 1 and sum/2 to obtain something like that [3 3 4]

S = 20;
n = 5;
m = 1;
while true
  P = ones(S+1,n);
  for in = n-1:-1:1
   P(:,in) = cumsum(P(:,in+1));
  end
  R = zeros(m,n);
  for im = 1:m
   s = S;
   for in = 1:n
    R(im,in) = sum(P(s+1,in)*rand<=P(1:s,in));
    s = s-R(im,in);
   end
  end
  x = find(R<=0);
  if x~=0
      continue
  else 
      break
  end
end
indMaxArry = ceil(n/2);
R = circshift(sort(R),[0,indMaxArry])

[John D'Errico]

Rather that trying to decipher what your this undocumented mess of code does, it would really help if you also explain what you want?

[Image Analyst]

"...have values between 1 and s/2 ..." <==== Did you overlook the second example in the documentation for rand()? The one that said "Random Numbers Within Specified Interval"?

[tlig zied]

at the beginning I use this code, but when we have, for example p=165 and c=80 it takes more time to generate the array

p=5;

c=3;

p1=randi([1 p],1,c);

while(sum(p1)~=p*2)

p1=randi([1 p],1,c);

end

[John D'Errico]

Do you want random INTEGERS with a fixed sum, or random floating point numbers?

In the cae of random floating point numbers, you could use one of two good tools on the file exchange, however, random integers with a fixed sum would be more difficult.

[tlig zied]

yes I want random INTEGERS

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/327656-conditional-random-number-generation#answer_257296

Answer 1

[Matt J]

This FEX submission would be applicable

https://www.mathworks.com/matlabcentral/fileexchange/9700-random-vectors-with-fixed-sum

[tlig zied]

I can't use it because of this constarint n*a <= s <= n*b

[Matt J]

You haven't told us what any of those symbols mean, but the FEX submission does support bounds on the array elements.