Monte-Carlo方法求解概率问题

n=21;   % number of players from nation A

m=32;   % number of games

nexp=100000;  % number of experiments

ninter=zeros(nexp,1); % number of games between A nation players

for j=1:nexp

    positions=zeros(m,2); % player nationality in each position

    for i=1:n

        ind=floor(rand(1,1)*(m*2-i+1))+1; % the index of a random available position

        ind1=find(positions==0,ind); % the absolute index in position matrix

        positions(ind1(end))=1;

    end

    ninter(j)=length(find(sum(positions,2)==2));

end

nmax=max(ninter);

p=histc(ninter,0:nmax)/nexp;