- #1
skrat
- 748
- 8
Function [itex]f(t)=\frac{t-i}{t+i}[/itex] for [itex]t\in \mathbb{R}[/itex] maps real ax into complex circle. Show that for any hermitian operator [itex]H[/itex] operator [itex]U:=(H-iI)(H+iI)^{-1}[/itex] is unitary (where [itex]H+iI[/itex] is reversible)
If I understand correctly [itex]U[/itex] is unitary when [itex]U=U^{T}[/itex] right?
So I tried to show that [itex]U[/itex] is unitary like this (hopefully it is ok):
[itex]U=(H-iI)(H+iI)^{-1}[/itex] because H hermitian than [itex]H^{*}=H[/itex]
[itex]U=(H^{*}-iI)(H^{*}+iI)^{-1}[/itex] but Identity does not change if I conjugate it and transpose it
[itex]U=(H^{*}-iI^{*})(H^{*}+iI^{*})^{-1}=((H-iI)^{-1}(H+iI))^{*}[/itex]
[itex]U=((H+iI)^{-1}(H-iI))^{T}[/itex] so [itex]U=U^{T}[/itex]
Right or wrong?
Than I have to calculate the inverse function [itex]f^{-1}=(\zeta ))i\frac{1+\zeta }{1-\zeta } [/itex] and show that [itex]f^{-1}(U)[/itex] is hermitian operator for any unitary operator [itex]U[/itex], where [itex]I-U[/itex] is reversible operator.
And here I have no idea how to start... :/
If I understand correctly [itex]U[/itex] is unitary when [itex]U=U^{T}[/itex] right?
So I tried to show that [itex]U[/itex] is unitary like this (hopefully it is ok):
[itex]U=(H-iI)(H+iI)^{-1}[/itex] because H hermitian than [itex]H^{*}=H[/itex]
[itex]U=(H^{*}-iI)(H^{*}+iI)^{-1}[/itex] but Identity does not change if I conjugate it and transpose it
[itex]U=(H^{*}-iI^{*})(H^{*}+iI^{*})^{-1}=((H-iI)^{-1}(H+iI))^{*}[/itex]
[itex]U=((H+iI)^{-1}(H-iI))^{T}[/itex] so [itex]U=U^{T}[/itex]
Right or wrong?
Than I have to calculate the inverse function [itex]f^{-1}=(\zeta ))i\frac{1+\zeta }{1-\zeta } [/itex] and show that [itex]f^{-1}(U)[/itex] is hermitian operator for any unitary operator [itex]U[/itex], where [itex]I-U[/itex] is reversible operator.
And here I have no idea how to start... :/