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math.FA2026

Unbounded Antilinear Operators on Hilbert Spaces

Arup Majumdar

The paper introduces unbounded antilinear operators on Hilbert spaces and develops their fundamental theory. In particular, we establish a closed range theorem, a polar decompositi…

math.FA2025

Spectral Properties of Off Diagonal Block Linear Relations via Moore Penrose Inverses in Hilbert Spaces

Arup Majumdar

In this paper, we characterize the essential spectra and the resolvent set of the off-diagonal block linear relation \[ \begin{bmatrix} 0 & A \\ B & 0 \end{bmatrix} \] in terms of…

math.FA2025

Hyers-Ulam stability of closed linear relations in Hilbert spaces

Arup Majumdar

This paper introduces the concept of Hyers-Ulam stability for linear relations in normed linear spaces and presents several intriguing results that characterize the Hyers-Ulam stab…

math.FA2024

On the generalized Cauchy dual of closed operators in Hilbert spaces

Arup Majumdar, P. Sam Johnson, Ram N. Mohapatra

In this paper, we introduce the generalized Cauchy dual of a closed operator with the closed range between Hilbert spaces and present intriguing fi…

math.FA2024

Characterizations of closed EP operators on Hilbert spaces

Arup Majumdar, P. Sam Johnson

In this paper, we present intriguing findings that characterize both the closed (unbounded) and bounded EP operators on Hilbert spaces. Additionally, we demonstrate the result $γ(T…

math.FA2024

The Moore-Penrose inverses of unbounded closable operators and the Cartesian product of closed operators in Hilbert spaces

Arup Majumdar, P. Sam Johnson

In this paper, we present some interesting results to characterize the Moore-Penrose inverses of unbounded closable operators and the Cartesian product of closed operators in Hilbe…