Spectrum (Operator)
Let 
be an Operator on a Hilbert Space. The spectrum 
of is the set of 
such that
is not invertible on all of the Hilbert Space, where the s are ComplexNumbers and 
is the Identity Operator. The definition can also be stated in terms of the resolventof an operator
and then the spectrum is defined to be the complement of
in the Complex Plane. It is easy todemonstrate that is an Open Set, which shows that the spectrum is closed (in fact, it is evencompact).See also Hilbert Space- Decreasing Sequence
- Decreasing Series
- Dedekind Cut
- Dedekind Eta Function
- Dedekind Function
- Dedekind Ring
- Dedekind's Axiom
- Dedekind's Problem
- Dedekind Sum
- Deducible
- Deep Theorem
- Defective Matrix
- Defective Number
- Deficiency
- Deficient Number
- Definable Set
- Defined
- Definite Integral
- Degenerate
- Degree
- Degree (Algebraic Surface)
- Degree (Map)
- Degree of Freedom
- Degree (Polynomial)
- Degree Sequence