N = 30;
X = zeros(2,N);

y = [0.9 0.1];
x = [0.25 0.75];
m = [0 0];

for i = 1:N
    X(:,i) = x;
    
    pm = m;
    m = x .* y;
    m = m ./ sum(m);
    m = (m + pm) / 2;

    px = x;    
    x = [m(2) m(1)];
    x = (x + px) / 2;
end

plot(X(1,:)); hold all;
plot(X(2,:)); axis([1 N 0 1]);