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> The Holder continuity condition looks sorta like the limit definition of a derivative with an exponent on the denominator. This is actually stronger than the
by vitus 5y ago
> The Holder continuity condition looks sorta like the limit definition of a derivative with an exponent on the denominator.
This is actually stronger than the epsilon-delta definition of continuity, as noted in the wiki article -- "For any α > 0, the condition implies the function is uniformly continuous."
Normally, you'd have something like
For all ϵ > 0, there exists δ(x, ϵ) > 0 such that
if |x - x₀| < δ, then |f(x) - f(x₀)| < ϵ.
(namely, at any given point, there's a ball of nearby points such that all their corresponding outputs are close together.)
But, with absolute continuity, δ is purely a function of ϵ, namely, that ball doesn't change size even as we move further away.
For instance, f(x)=x is absolutely continuous, while f(x)=x^2 is not. (for the former case, we can use δ = ϵ/2; for the latter case, we'd need a δ that looks something like 2ϵ·x)
In this case, since the Holder condition depends only on the distance between x and y, it automatically implies absolute continuity.
- jbrot 5y agoSmall correction: the definition you shared is that of “uniform continuity” [1] not “absolute continuity” [2]. Absolute continuity is a slightly stronger condition where instead of providing a single (x1, x2) pair with |x1 - x2| < delta, you can now provide a finite list of pairs. [1] https://en.m.wikipedia.org/wiki/Uniform_continuity https://en.m.wikipedia.org/wiki/Uniform_continuity [2] https://en.m.wikipedia.org/wiki/Absolute_continuity https://en.m.wikipedia.org/wiki/Absolute_continuity
- vitus 5y agoAh, good catch! The wiki quote that I cited does reference uniform continuity, so the rest still holds. (left for posterity so your comment makes sense)