On the reconstruction and sampling of random fields based on information
from limited-size marginals
Abstract
In an ideal application of sequential simulation, parameters are
simulated one at a time conditioned to all previously simulated
parameters. This requires that marginal distributions of all dimensions
(used to derive the conditional distributions) from the random field can
be extracted and used for the simulation. However, in practice, only
incomplete information from limited-size marginals is used for
sequential simulation due to, e.g., computational unwieldiness or to
ensure adequate pattern statistics. In this paper, we start out by
addressing the problem of how to reconstruct an unknown random field
that is consistent with known limited-size marginals. This problem turns
out to be highly underdetermined (i.e., infinitely many solutions
exist). Therefore, we describe possible additional constraints to
supplement the marginals in order to reconstruct well-defined random
fields. Secondly, we investigate which random field (out of infinitely
many) that is sampled by sequential simulation algorithms using
limited-size marginals. We show that sample distributions of such
algorithms may depend on the sampling sequence and, sometimes, are
inconsistent with the known marginals. We reviewed a formulation of a
Markov random field that provides a well-defined solution to the
underdetermined problem. Finally, we investigate the relation between
marginal-size and information content of reconstructed random fields.