// tendance linéaire + saisonalité de période mensuelle
function X = simul_decomp(alpha0, alpha1, b, T)
  t = (1:T);
  epsilon = rand(1, T, 'normal');
  k=floor(T/12)-1;
  if k>0 then
    for i=0:k
      B(i*12+1:12*(i+1)) = b;
    end
    k=k+1;
    if k*12 < T then
//      pause
      B(k*12+1:T) = b(1:T-k*12);
    end
  else
    B(1:T) = b(1:T);
  end
  X = epsilon + alpha0 + alpha1 * t + B;
endfunction