and similarly for the others. Here, E[•] denotes the expectation value and ⊗ the tensor product, that is, in this case, multiplying the i-th with the j-th component of the vector ( f 2 -f t 2 ) to obtain a matrix. We know that the true model satisfies F t 2 = M( f t 2 , r 1 , r 2 ) subject to equation . Finally, a parameter vector θ = (r 1 , r 2 ) T is defined for less clutter, in general this would be a d-dimensional vector. For the case of reactivity ratio estimation, d = 2 as we aim for determine two estimators (r 1 , r 2 ).