Abstract. For two given orthogonal projectors $P_A$ and $P_B$ of the same order, we investigate how to express Moore--Penrose inverses of the differences $P_A - P_B$ and $P_AP_B - P_BP_A$, and then consider some related topics.

AMS Subject Classification (1991): 15A09, 15A24

Keyword(s): difference, Moore--Penrose inverse, weighted Moore--Penrose inverses, orthogonal projector

Received May 28, 2002, and in revised form February 6, 2003. (Registered under 2915/2009.)