integrals and the integrals you need to do it numerically and in high dimensions you can't do it precisely because you need to populate the high dimensional space to get a reasonable approximation your integral not gonna be able to do it or in a discrete space if your state space is very large imagine I don't know imagine a state variable has is a vector so X is a vector let's say x0 is a vector and each entering that x0 vector can take on I don't know 100 values and maybe 100 entries now you have 100 to 200 possible values for your