A definition of
frames for Krein
spaces is proposed, which extends the notion of -orthonormal bases of Krein
spaces. A -frame for a Krein
space is in particular a frame for in the Hilbert
space sense. But it is also compatible with the indefinite inner product , meaning that it determines a pair of maximal uniformly -definite sub
spaces, an analogue to the maximal dual pair associated to a -orthonormal basis.
Also, each -frame induces an indefinite reconstruction formula for the vectors in , which resembles the one given by a -orthonormal basis.