# New post in Operator-theory

## Are there non nilpotent operators with spectrum 0?

August 18th, 2022

## Proof explanation: convexity of the numerical range of an operator (Toeplitz-Hausdorff Theorem)

October 29th, 2020

## A operator is unitary if and only if it is a surjective isometry

September 8th, 2020

August 1st, 2022

August 1st, 2022

## Symmetric Square Root of Symmetric Invertible Matrix

August 17th, 2022

August 1st, 2022

## Prove $p^2=p$ and $qp=0$

October 31st, 2020

August 1st, 2022

August 1st, 2022

August 1st, 2022

August 1st, 2022

## Showing that the orthogonal projection in a Hilbert space is compact iff the subspace is finite dimensional

November 21st, 2020

August 1st, 2022

August 1st, 2022

August 1st, 2022

August 1st, 2022

## Unbounded linear operator

August 16th, 2022

## An introductory textbook on functional analysis and operator theory

August 13th, 2022

August 1st, 2022

August 1st, 2022

## Bounded operator that does not attain its norm

February 22nd, 2020

August 1st, 2022

## Two different definitions of ellipticity

August 25th, 2022

May 17th, 2020

## Matrix Representation of Operators in Infinite Dimensional (Separable) Hilbert Spaces

August 15th, 2022

August 1st, 2022

August 1st, 2022

August 1st, 2022

## If $A_n$ is a sequence of positive bounded linear operators converging in norm to $A$ on a Hilbert Space, show $\sqrt{A_n}\to\sqrt{A}$ in norm.

August 13th, 2022