Ziad Shihab

Reflexive Space -- from Wolfram MathWorld




Reflexive Space

Let be a normed space and denote the second dual vector space of . The canonical map defined by gives an isometric linear isomorphism (embedding) from into . The space is called reflexive if this map is surjective. This concept was introduced by Hahn (1927).

For example, finite-dimensional (normed) spaces and Hilbert spaces are reflexive. The space of absolutely summable complex sequences is not reflexive. James (1951) constructed a non-reflexive Banach space that is isometrically isomorphic to its second conjugate space.

Reflexive spaces are Banach spaces. This follows since given a normed space that may or may not be Banach, the norm on induces a norm (called the dual norm) on the dual of , and under the dual norm, is Banach. Iterating again, (the bidual of ) is also Banach, and since is reflexive if it coincides with its bidual, is Banach.

SEE ALSO: Banach Space, Dual Vector Space, Normed Space

Portions of this entry contributed by Mohammad Sal Moslehian

Portions of this entry contributed by Christopher Stover

REFERENCES:

Hahn, H. "Über lineare Gleichungssysteme in linearen Räumen." J. reine angew. Math. 157, 214-229, 1927.

James, R. C. "A Non-Reflexive Banach Space Isometric with Its Second Conjugate Space." Proc. Nat. Acad. Sci. USA 37, 174-177, 1951.

CITE THIS AS:

Moslehian, Mohammad Sal; Stover, Christopher; and Weisstein, Eric W. "Reflexive Space." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ReflexiveSpace.html

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