that way get an approximate estimate of the distribution and say yes absolutely in general these filter calculations are not possible to do exactly but in special cases discrete small number of values a state can take on yes very feasible and linear Gaussian distributions for a next state given current state and observation given current state again we can do it in closed form those are the only ones that are tractable the other ones you'll do approximations yes I say let me use this what's an example of a smoother being useful in that you