PhyslibAlpha.ProbabilisticTheory.HilbertSpace.TraceClass.Banach
The trace-class Banach space
i. Overview
The trace-class operators form a Banach space `𝒮₁(H)` under the trace norm. The trace norm dominates the operator norm, so an absolutely convergent series of trace-class operators converges in operator norm. Its limit is trace class because the trace norm is lower semicontinuous along such limits, which gives completeness.
ii. Key results
- `TraceClass` : the trace-class operators with the trace norm. - `opNorm_le_traceNorm` : the operator norm is at most the trace norm. - `isTraceClass_of_tendsto_of_traceNorm_bounded` : an operator-norm limit of trace-class operators with bounded trace norms is trace class. - `TraceClass.instCompleteSpace` : `𝒮₁(H)` is complete.
iii. Table of contents
- A. Arithmetic closure of `IsTraceClass`
- B. The trace-class submodule and Banach space
A. Arithmetic closure of `IsTraceClass`
B. The trace-class submodule and Banach space
21 declarations
The zero operator is trace-class
The zero operator on a Hilbert space is trace-class.
Scalar multiples of trace-class operators are trace-class
Let be a complex Hilbert space and be a continuous linear operator. For any complex scalar , if is a trace-class operator, then the scalar multiple is also a trace-class operator.
If is trace-class, then is trace-class
Let be a complex Hilbert space and be a bounded linear operator. If is a trace-class operator, then its negation is also a trace-class operator.
for the zero operator
Let be a complex Hilbert space. The trace norm of the zero operator is equal to , i.e., .
Absolute Homogeneity of the Trace Norm:
Let be a complex Hilbert space and be a continuous linear operator. For any complex scalar , if is a trace-class operator, then the trace norm of the scalar multiple is equal to the product of the absolute value of and the trace norm of : where denotes the trace norm.
for trace-class operators
Let be a complex Hilbert space and let be a continuous linear operator. If is a trace-class operator, then its negation is also a trace-class operator, and the trace norm of is equal to the trace norm of , i.e., .
Operator Norm is Bounded by Trace Norm:
For any trace-class operator on a complex Hilbert space , the operator norm is less than or equal to the trace norm .
-submodule of trace-class operators on
Let be a complex Hilbert space and let (represented as `H →L[ℂ] H`) be the space of bounded linear operators on . The `traceClassSubmodule` is the -submodule of consisting of all trace-class operators. It is defined by showing that the zero operator is trace-class, and that the property of being trace-class is preserved under operator addition and scalar multiplication by complex numbers .
Trace-class Banach space
Let be a complex Hilbert space. The trace-class Banach space is the space consisting of all trace-class bounded linear operators on , equipped with the trace norm .
is an additive abelian group
Let be a complex Hilbert space. The space of trace-class operators forms an additive abelian group under the standard addition of operators. This structure provides the definition for the sum of two trace-class operators, the zero operator, and the additive inverse (negation) of a trace-class operator within the space .
is a vector space over
Let be a complex Hilbert space. The space of trace-class operators forms a vector space (module) over the field of complex numbers . This structure defines the scalar multiplication of a trace-class operator by a complex number, such that for any and , the operator is also an element of .
Let be a complex Hilbert space and be a bounded linear operator. belongs to the trace-class submodule of if and only if is a trace-class operator.
Elements of are trace-class operators
Let be a complex Hilbert space and let (denoted in the formal text as `TraceClass H`) be the Banach space of trace-class operators on . For any element , the underlying bounded linear operator is a trace-class operator.
Construction of an element in from a trace-class operator
Given a bounded linear operator on a complex Hilbert space and a proof that is trace-class (i.e., satisfies `IsTraceClass T`), this function returns as an element of the trace-class Banach space .
The underlying operator of a constructed trace-class element is the original operator
Let be a complex Hilbert space and be the space of bounded linear operators on . For any operator that is trace-class, the underlying bounded linear operator of the element in the trace-class space constructed from (via `ofOperator`) is equal to .
Trace norm is an `AddGroupNorm` on
Let be a complex Hilbert space and let be the space of trace-class operators on . The trace norm satisfies the axioms of an additive group norm (`AddGroupNorm`) on . Specifically, for all operators , the following properties hold: - **Identity**: . - **Negation**: . - **Triangle Inequality**: . - **Definiteness**: implies . This is established by the fact that the operator norm is dominated by the trace norm (), so if the trace norm vanishes, the operator itself must be zero.
is a normed additive abelian group
Let be a complex Hilbert space. The space of trace-class operators is a normed additive abelian group, where the norm of an operator is defined as the trace norm .
The norm on is the trace norm
Let be a complex Hilbert space and let denote the Banach space of trace-class operators on . For any operator , the norm in the space is equal to the trace norm .
is a normed space over
Let be a complex Hilbert space. The space of trace-class operators is a normed space over the field of complex numbers with respect to the trace norm . This structure implies that scalar multiplication is compatible with the norm, such that for any and , the identity holds.
Lower Semicontinuity of the Trace Norm with respect to Operator-Norm Convergence
Let be a Hilbert space. Let be a sequence of continuous linear operators on , and let be a continuous linear operator on . Suppose that for every , is a trace-class operator whose trace norm is bounded by a constant (i.e., for all ). If converges to in the operator norm as , then is also a trace-class operator and its trace norm satisfies .
The trace-class space is a complete space
Let be a complex Hilbert space. The space of trace-class operators on , equipped with the trace norm , is a complete metric space. Consequently, since is a normed space, it is a Banach space.
