Importance sampling, Fokker-Planck and Langevin equations

If we assume a discrete set of events, our initial probability distribution function can be given by

wi(0)=δi,0,

and its time-development after a given time step Δt=ϵ is

wi(t)=jW(ji)wj(t=0).

The continuous analog to wi(0) is

w(x)δ(x),

where we now have generalized the one-dimensional position x to a generic-dimensional vector x. The Kroenecker δ function is replaced by the δ distribution function δ(x) at t=0.