释义 |
Whitney-Mikhlin Extension ConstantsN.B. A detailed on-line essay by S. Finchwas the starting point for this entry.
Let be the -D closed Ball of Radius centered at the Origin. A function which isdefined on is called an extension to of a function defined on if
 | (1) |
Given 2 Banach Spaces of functions defined on and , find the extension operator fromone to the other of minimal norm. Mikhlin (1986) found the best constants such that this condition, correspondingto the Sobolev integral norm, is satisfied, | |  | (2) |
. Let
 | (3) |
then for ,
 | (4) |
where is a Modified Bessel Function of the First Kind and is a Modified Bessel Functionof the Second Kind. For , | |  | (5) | For ,
 | (6) |
which is bounded by
 | (7) |
For Odd , the Recurrence Relations
with
where e is the constant 2.71828..., give
 | (14) |
The first few are
Similar formulas can be given for even in terms of , , , . References
Finch, S. ``Favorite Mathematical Constants.'' http://www.mathsoft.com/asolve/constant/mkhln/mkhln.html Mikhlin, S. G. Constants in Some Inequalities of Analysis. New York: Wiley, 1986.
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