possible for such for-loop to be vectorized?

Hello all, I'm attempting to speed up my for-loop which performs something akin to Gaussian elimination in a iterative way, since it has to be implemented in simulink, i went for for-loop instead of recursive function. Could anyone give me some hint on how to possibly vectorize it? Simplified code for illustration. Thanks in advance.

function Uopt = forloop(sq_r,Uunc,H)   % where H is 3-by-3 lower triangular matrix,Uunc 3-by-1 vector
Uopt = NaN(3,1);
U = NaN(3,1);
for i = 0:1
    U(1) = i;
    sq_dnew = (Uunc(1) - H(1,1:1)*U(1:1))^2;
    if sq_dnew <= sq_r
       sq_d1 = sq_dnew;
       for j = 0:1
           U(2) = j;
           sq_dnew = (Uunc(2) - H(2,1:2)*U(1:2))^2 + sq_d1;
           if sq_dnew <= sq_r
              sq_d2 = sq_dnew;
              for k = 0:1
                  U(3) = k;
                  sq_dnew = (Uunc(3) - H(3,1:3)*U(1:3))^2 + sq_d2;
                  if sq_dnew <= sq_r
                     sq_r = sq_dnew;
                     Uopt = U;
                  end
              end
          end
      end
   end
end