- #1
Oxymoron
- 870
- 0
Im considering a complex Hilbert space. Then define a relation [itex]\preceq[/itex] on the set of all self-adjoint, bounded, linear operators (denote by A) by
[tex]S \preceq T \, \Leftrightarrow \langle Sx\,|\,x \rangle \leq \langle Tx\,|\,x \rangle[/tex]
for all [itex]x \in \mathcal{H}[/itex].
Now I want to prove that [itex]\preceq[/itex] is a partial order on [itex]A[/itex], for all [itex]T \in A[/itex] such that
[tex]-\|T\|I \leq T \leq \|T\|I[/tex].
Now to prove that a relation is a partial order then it must satisfy three things:
1. [tex]T \preceq T[/tex] for all [tex]T \in A[/tex]
2. If [tex]T \preceq S[/tex] and [tex]S \preceq T[/tex], then [tex]T = S[/tex] for all [tex]S,T \in A[/tex].
3. If [tex]T \preceq S[/tex] and [tex]S \preceq U[/tex], then [tex]T \preceq U[/tex], for all [tex]S,T,U \in A[/tex].
This relation says that a self-adjoint, bounded, linear operator is greater than another operator of the same category if and only if the inner product of that operator with an arbitrary element in the complex Hilbert space is larger.
So to prove 1. we have to show that [itex]T \leq T[/itex] if and only if [itex]\langle Tx\,|\,x \rangle \leq \langle Tx\,|\,x \rangle[/itex]. Well, quite obviously, [itex]\langle Tx\,|\,x \rangle = \langle Tx\,|\,x \rangle[/itex], for any choice of [itex]x\in\mathcal{H}[/itex] and for any S-A,B,L operator on complex Hilbert space. Therefore (1) is proved.
How does this sound so far?
[tex]S \preceq T \, \Leftrightarrow \langle Sx\,|\,x \rangle \leq \langle Tx\,|\,x \rangle[/tex]
for all [itex]x \in \mathcal{H}[/itex].
Now I want to prove that [itex]\preceq[/itex] is a partial order on [itex]A[/itex], for all [itex]T \in A[/itex] such that
[tex]-\|T\|I \leq T \leq \|T\|I[/tex].
Now to prove that a relation is a partial order then it must satisfy three things:
1. [tex]T \preceq T[/tex] for all [tex]T \in A[/tex]
2. If [tex]T \preceq S[/tex] and [tex]S \preceq T[/tex], then [tex]T = S[/tex] for all [tex]S,T \in A[/tex].
3. If [tex]T \preceq S[/tex] and [tex]S \preceq U[/tex], then [tex]T \preceq U[/tex], for all [tex]S,T,U \in A[/tex].
This relation says that a self-adjoint, bounded, linear operator is greater than another operator of the same category if and only if the inner product of that operator with an arbitrary element in the complex Hilbert space is larger.
So to prove 1. we have to show that [itex]T \leq T[/itex] if and only if [itex]\langle Tx\,|\,x \rangle \leq \langle Tx\,|\,x \rangle[/itex]. Well, quite obviously, [itex]\langle Tx\,|\,x \rangle = \langle Tx\,|\,x \rangle[/itex], for any choice of [itex]x\in\mathcal{H}[/itex] and for any S-A,B,L operator on complex Hilbert space. Therefore (1) is proved.
How does this sound so far?