Let E be a Banach space contained in a Hilbert space L. Assume thatthe inclusion is continuous with dense range. Following the terminology of Gohberg andZambicki, we say that a bounded operator on E is a proper operator ...

Let H be a complex Hilbert space. We study the relationships between the angles between closed subspaces of H, the oblique projections associated to non direct decompositions of H and a notion of compatibility between a ...

Let A be a positive injective operator in a Hilbert space View the MathML source, and denote by View the MathML source the inner product defined by A : [f,g]=〈Af,g〉. A closed subspace S⊂H is called A -compatible if ...

We study A-projections, i.e. operators on a Hilbert space H which act as projections when a seminorm is considered in H. The A-projections were introduced by Mitra and Rao (1974) for finite-dimensional spaces. We relate ...

Let H be a (separable) Hilbert space and {e_k}_k >=1 a fixed orthonormal basis of H. Motivated by many papers on scaled projections, angles of subspaces and oblique projections, we define and study the notion of compatibility ...

In a recent article, Smale and Zhou define a notion of rich data for sampling problems and reconstruction of signals from a discrete set of samples and study different least-square problems related with the minimization ...