The antithetic variates technique consists, for every sample path obtained,
in taking its antithetic path - that is given a path
\(\varepsilon_1,\dots,\varepsilon_M\) to also take, for
example, \(-\varepsilon_1,\dots,-\varepsilon_M\) or
Importance sampling is a general technique for estimating properties of a
particular distribution, while only having samples generated from a different
distribution rather than the distribution of interest.