  We apply the computational methodology of phase retrieval to the problem of
folding heteropolymers. The ground state fold of the polymer is defined by the
intersection of two sets in the configuration space of its constituent
monomers: a geometrical chain constraint and a threshold constraint on the
contact energy. A dynamical system is then defined in terms of the projections
to these constraint sets, such that its fixed points solve the set intersection
problem. We present results for two off-lattice HP models: one with only
rotameric degrees of freedom, and one proposed by Stillinger et al. with
flexible bond angles. Our phase retrieval inspired algorithm is competitive
with more established algorithms and even finds lower energy folds for one of
the longer polymer chains.
