Resolvent set
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In linear algebra and operator theory, the resolvent set of a linear operator is a set of complex numbers for which the operator is in some sense "well-behaved". The resolvent set plays an important role in the resolvent formalism.
Definitions
Summarize
Perspective
Let X be a Banach space and let be a linear operator with domain . Let id denote the identity operator on X. For any , let
A complex number is said to be a regular value if the following three statements are true:
- is injective, that is, the corestriction of to its image has an inverse called the resolvent;[1]
- is a bounded linear operator;
- is defined on a dense subspace of X, that is, has dense range.
The resolvent set of L is the set of all regular values of L:
The spectrum is the complement of the resolvent set
and subject to a mutually singular spectral decomposition into the point spectrum (when condition 1 fails), the continuous spectrum (when condition 2 fails) and the residual spectrum (when condition 3 fails).
If is a closed operator, then so is each , and condition 3 may be replaced by requiring that be surjective.
Properties
- The resolvent set of a bounded linear operator L is an open set.
- More generally, the resolvent set of a densely defined closed unbounded operator is an open set.
Notes
References
External links
See also
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