n (typically the origin). Users
can provide a variogram function that takes distance as argument and is
vectorized. If <code>vario</code> is provided, the model will simulate
from an intrinsically stationary Gaussian process. The user can
alternatively provide a covariance matrix <code>sigma</code> obtained by
conditioning on a site, in which case simulations are from a stationary
Gaussian process. See <span class="citation">Engelke et al.
(2015)</span> or <span class="citation">Dombry, Engelke, and Oesting