Bounded operators and continuous duals
Research context
postgraduate concept · established · As of 2026-10-10
A linear map T:X→Y between normed spaces is continuous exactly when ||Tx|| ≤ C||x|| for some finite C.
Key knowledge
A linear map T:X→Y between normed spaces is continuous exactly when ||Tx|| ≤ C||x|| for some finite C. Its operator norm is sup over unit vectors of ||Tx||. The continuous dual X* contains bounded linear functionals; arbitrary algebraic functionals need not be continuous in infinite dimensions. If Y is Banach then bounded operators X→Y form a Banach space in this norm.
Values and equations
||T|| = sup{||Tx|| : ||x|| ≤ 1}
- T
- Linear map from X to Y
- ||·||
- Specified norms on domain and codomain
Conditions and scope
- T is defined on all of X for this bounded-operator equivalence; a densely defined unbounded differential operator needs a separate domain.
- Use the continuous dual, not the unrestricted algebraic dual.
Sources · 1
References
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Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: Lecture 2: continuity, operator norm and dual spaces. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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- research-math-bounded-operator-norm
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- research.1
- Structured reference record
- Postgraduate & research reference