If \(X(t)\) is a stationary increments process, then \(\Delta X_0, \Delta X_1, \ldots\) with
$$
\Delta X_n = X((n+1)\Delta t) - X(n \Delta t)
$$
is a stationary time series. This function converts the ACF of this series into the MSD of the corresponding positions, namely returns the sequence \(\eta_1, \ldots, \eta_N\), where \(\eta_i = \mathrm{var}(X(i\Delta t))\).