Extreme points and identification of optimal alternate dual frames

The main purpose of this paper is to identify the set of optimal dual frames under erasures. To this end, we characterize extreme points in the set of all optimal duals for 1-erasure. Also, we give some conditions under which an alternate dual frame is either not optimal or is a non-unique optimal dual. Moreover, we obtain a new characterization of frames when the canonical dual is the unique optimal dual frame for erasures.