function [x,rvec] = myCG(A, b, x0, max_itr, tol)
    x = x0;
    rvec = zeros(1,max_itr+1);
    r = b - A * x0;
    rvec(1) = norm(r, 2);
    d = r;
    delta_old = dot(r, r);
    
    for i = 1:max_itr
        s = A * d;
        alpha = delta_old / dot(d, s);
        x = x + alpha * d;
        r = r - alpha * s;
        delta_new = dot(r, r);
        beta = delta_new / delta_old;
        d = r + beta * d;
        delta_old = delta_new;
        rvec(i + 1) = delta_new; 
        
        if delta_new / norm(b) < tol
            rvec = rvec(1:i+1);
            break
        end
    end
end