  Phase retrieval can be expressed as one non-convex constrained optimization
problem to identify one phase minimizer in the primal space. Many iterative
transform techniques have been proposed to identify the minimizer, e.g.,
relaxed averaged alternating reflections(RAAR) algorithms. RAAR algorithm is
one alternating direction method of multipliers(ADMM) with one penalty
parameter. Pairing with multipliers (dual vectors), phase vectors are lifted to
higher dimensional vectors, RAAR algorithms actually is one continuation
algorithm, which searches for local Nash equilibria in a primal-dual space. The
dual iteration approximates one gradient ascent flow, which drives the
corresponding local minimizers in a positive-definite Hessian region. The
penalty parameter, which is the reciprocal of the RAAR parameter, plays a role
of altering the size of the attractor basin for each stationary point. Under
proper penalty parameters, the RAAR avoids the stagnation of these
corresponding local minimizers in the primal space and thus screens out many
stationary points corresponding to non-local minimizers.
