“…Hence, in the subsequent interval [∆t, t + ∆t], the particle starts either from x 0 (the former case) or from x + dx (the latter case). Taking into account all these possibilities, we have G r (x, y, k, t + ∆t) = r∆tG r (x 0 , y, k, t) + (1 − r∆t)e −kU (x)∆t G r (x + ∆x, y, k, t) ∆x , with U(x) = δ(x − y) , (7) where the expectation on the second term is taken on different noise realizations [33,34]. We note that the term exp(−kU(x)∆t) above is somewhat ambiguous since powers of a delta function are not well defined.…”