This approximation not only facilitates the computation of Eq (7), but also means that p(z 2 , c 2 |c 1 , z 1 ) no longer depends on z 1 and c 1 .
eq (7) can be approximated as Now that p(z 0 , c 0 ) and p(z 2 , c 2 ) are both out of the summation; they can be pre-computed and cached.