Top Qs
Timeline
Chat
Perspective
Schwartz space
Function space of all functions whose derivatives are rapidly decreasing From Wikipedia, the free encyclopedia
Remove ads
In mathematics, Schwartz space is the function space of all functions whose derivatives are rapidly decreasing. This space has the important property that the Fourier transform is an automorphism on this space. This property enables one, by duality, to define the Fourier transform for elements in the dual space of , that is, for tempered distributions. A function in the Schwartz space is sometimes called a Schwartz function.

Schwartz space is named after French mathematician Laurent Schwartz.
Remove ads
Definition
Let be the set of non-negative integers, and for any , let be the n-fold Cartesian product.
The Schwartz space or space of rapidly decreasing functions on is the function spacewhere is the function space of smooth functions from into , and Here, denotes the supremum, and we used multi-index notation, i.e. and .
To put common language to this definition, one could consider a rapidly decreasing function as essentially a function such that , all exist everywhere on and go to zero as faster than any reciprocal power of . In particular, is a subspace of .
Remove ads
Examples of functions in the Schwartz space
- If is a multi-index, and a is a positive real number, then
- Any smooth function with compact support is in . This is clear since any derivative of is continuous and supported in the support of , so ( has a maximum in by the extreme value theorem.
- Because the Schwartz space is a vector space, any polynomial can be multiplied by a factor for a real constant, to give an element of the Schwartz space. In particular, there is an embedding of polynomials into a Schwartz space.
Remove ads
Properties
Analytic properties
- From Leibniz's rule, it follows that is also closed under pointwise multiplication:
In particular, this implies that is an -algebra. More generally, if and is a bounded smooth function with bounded derivatives of all orders, then .
- The Fourier transform is a linear isomorphism .
- If then is Lipschitz continuous and hence uniformly continuous on .
- is a distinguished locally convex Fréchet Schwartz TVS over the complex numbers.
- Both and its strong dual space are also:
Relation of Schwartz spaces with other topological vector spaces
- If , then is a dense subset of .
- The space of all bump functions, , is included in .
Remove ads
See also
References
Wikiwand - on
Seamless Wikipedia browsing. On steroids.
Remove ads