In mathematics, a Ditkin set, introduced by , is a closed subset of the
circle
A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. Equivalently, it is the curve traced out by a point that moves in a plane so that its distance from a given point is const ...
such that a
function
Function or functionality may refer to:
Computing
* Function key, a type of key on computer keyboards
* Function model, a structured representation of processes in a system
* Function object or functor or functionoid, a concept of object-orie ...
''f'' vanishing on the
set can be approximated by functions φ
''n''''f'' with φ vanishing in a neighborhood of the set.
References
*{{Citation , last1=Ditkin , first1=V. , title=On the structure of ideals in certain normed rings , mr=0002012 , year=1939 , journal=Uchenye Zapiski Moskov. Gos. Univ. Matematika , volume=30 , pages=83–130
Mathematical analysis