  The reduced density matrix (RDM) is a fundamental contraction of the
Bose-Einstein condensate wave function, encapsulating its one-body properties.
It serves as a major analysis tool with which the condensed component of the
density can be identified. Despite its cardinal importance, calculating the
ground-state RDM of trapped interacting bosons is challenging and has been
fully achieved only for specific models or when the pairwise interaction is
weak. In this paper we discuss a new approach to compute the RDM based on a
double-walker diffusion Monte Carlo random walk coupled with a stochastic
permanent calculation. We here describe the new method and study some of its
statistical convergence and properties applying it to some model systems.
