  We show that the dark soliton of the Gross-Pitaevskii equation (GPE) that
describes the Bose-Einstein condensate (BEC) density of a system of weakly
repulsive bosons, also describes that of a system of strongly repulsive hard
core bosons at half filling. This connection establishes a relationship between
the GPE soliton and the magnetic soliton of an easy-plane ferromagnet, where
the BEC density relates to the square of the in-plane magnetization of the
system. This mapping between well known solitons in two distinct physical
systems provides an intuitive understanding of various characteristics of the
solitons.
