A new formula for the weighted Moore-Penrose inverse and its applications

Abstract

In the general setting of the adjointable operators on Hilbert $C^{\ast }$-modules, this paper deals mainly with the weighted Moore-Penrose (briefly weighted M-P) inverse $A_{MN}^{†}$ in the case that the weights $M$ and $N$ are self-adjoint invertible operators, which need not to be positive. A new formula linking $A_{MN}^{†}$ to $A$, $A^{†}$, $M$ and $N$ is derived, in which $A^{†}$ denotes the M-P inverse of $A$. Based on this formula, some new results on the weighted M-P inverse are obtained. Firstly, it is shown that $A_{MN}^{†}=A_{ST}^{†}$ for some positive definite operators $S$ and $T$. This shows that $A_{MN}^{†}$ is essentially an ordinary weighted M-P inverse. Secondly, some limit formulas for the ordinary weighted M-P inverse originally known for matrices are generalized and improved. Thirdly, it is shown that when $A,M$ and $N$ act on the same Hilbert $C^{\ast }$-module, $A_{MN}^{†}$ belongs to the $C^{\ast }$-algebra generated by $A$, $M$ and $N$. Finally, some characterizations of the continuity of the weighted M-P inverse are provided.