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oscillation of a function (Definition)
Definition   Let $f:X\subset\mathbb{R}\to\mathbb{R}$ The oscillation of the function $f$ on the set $X$ is said to be $$\omega(f,X)=\sup_{a,b\,\in\, X}|f(b)-f(a)|,$$ where $a, b$ are arbitrary points in $X$

Examples

  • $\omega(x^2, \, [-1,2])=4$
  • $\omega(x, \, [-1,2])=3$
  • $\omega(x, \, (-1,2))=3$
  • $\omega(\sgn x \, [-1,2])=2$
  • $\omega(\sgn x \, [0,2])=1$
  • $\omega(\sgn x \, (0,2])=0$
Cauchy's criterion can be expressed in terms of this concept.[1]

Bibliography

1
V., Zorich, Mathematical Analysis I, pp. 131, First Ed., Springer-Verlag, 2004.




"oscillation of a function" is owned by perucho. [ full author list (2) ]
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See Also: total variation


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Cauchy criterion for the existence of a limit of a function (Theorem) by perucho
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Cross-references: terms, points, function

This is version 2 of oscillation of a function, born on 2008-01-27, modified 2008-04-09.
Object id is 10217, canonical name is OscillationOfAFunction.
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Classification:
AMS MSC26A06 (Real functions :: Functions of one variable :: One-variable calculus)

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some additions? by perucho on 2008-01-27 09:01:49
Hi Jussi,
>It could be better to write X \subseteq R, since often one thinks that \subset means a proper inclusion.
Well yes, it's a proper inclusion because X could be very small as it is usually included in a sequence of subsets, for instance, a filter basis. In fact this concept is useful to define limit of a function.
> Some mentioning of applications of oscillation?
>What Cauchy's criterion do you mean?
I did put an entry on this theorem. I think this is an interesting approach so I decided to include it in PM.
Cheers my dear friend,
Pedro


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