  This work takes the first steps towards solving the "phaseless subspace
tracking" (PST) problem. PST involves recovering a time sequence of signals (or
images) from phaseless linear projections of each signal under the following
structural assumption: the signal sequence is generated from a much lower
dimensional subspace (than the signal dimension) and this subspace can change
over time, albeit gradually. It can be simply understood as a dynamic
(time-varying subspace) extension of the low-rank phase retrieval problem
studied in recent work.
