Ground state of trapped interacting Bose-Einstein condensates by an explicit imaginary-time algorithm

We show that an explicit time-marching method previously developed for the numerical study of the dynamics of Bose-Einstein condensates can be profita bly adapted to the numerical determination of their ground state. After red uction to a one-dimensional model, we first reproduce and test known result s on condensates in harmonic traps and then determine the ground state of a condensate in a harmonically bound optical lattice in the range of paramet ers which are relevant to existing experiments.