P = [0  1/100 -1/50 1/80 -1/280 0];
t = [400 20 40 30 499.027];
j = length(t);
y = zeros(1,j+1);
u = zeros(1,j+1);
y(j+1) = 0.0;
u(j+1) = 0.1;
% reverse yu trace
for k = j:-1:1
    u(k) = u(k+1) + y(k+1)*P(k+1);
    y(k) = y(k+1) - u(k)*t(k);
end
YU = [y' u']

