Given a complex Krein space H with fundamental symmetry J, the aim of this note is to characterize the set of J-normal projections Q={Q∈L(H):Q2=QandQ#Q=QQ#}. The ranges of the projections in QQ are exactly those ...

A J-frame for a Krein space H is in particular a frame for H (in the Hilbert space sense). But it is also compatible with the indefinite inner-product of H, meaning that it determines a pair of maximal uniformly definite ...

The aim of this work is to generalize the notions of Schur complements and shorted operators to Krein spaces. Given a (bounded) J-selfadjoint operator A (with the unique factorization property) acting on a Krein space H ...

Given B,C and W operators in the algebra L(H) of bounded linear operators on the Krein space H, the minimization problem min (BX − C)^{#}W(BX − C), for X ∈ L(H), is studied when the weight W is selfadjoint. The analogous ...