On the connection between classes of functions of bounded variation and classes of functions with fractal graph
D. I. Masyutin N.N. Krasovskii Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg
Abstract:
For a real-valued function
$f$ continuous on a closed interval, the modulus of fractality
$\nu(f, \varepsilon)$ is defined for every
$\varepsilon > 0$ as the minimum number of squares with sides of length
$\varepsilon$ parallel to the coordinate axes that can cover the graph of
$f$. For a nonincreasing function
$\mu: (0, +\infty) \to (0, +\infty)$, we consider the class
$F^{\mu}$ of functions continuous on a closed interval and such that
$\nu(f, \varepsilon) = O(\mu(\varepsilon))$. The relationship between the classes
$F^{\mu_1}$ and
$F^{\mu_2}$ is described for various
$\mu_1$ and
$\mu_2$. A connection is established between the classes
$F^{\mu}$ and the classes of continuous functions of bounded variation
$BV_{\Phi}[a, b] \cap C[a, b]$ for arbitrary convex functions
$\Phi$. Namely, there is an inclusion
$$ BV_{\Phi}[a,b] \cap C[a,b] \subset F^{\frac{\Phi^{\,-1}(\varepsilon)}{\varepsilon^2}}. $$
A counterexample is constructed showing that this inclusion cannot be improved. It is further shown that the equality of the classes
$F^{\mu}$ and
$BV_{\Phi}[a,b] \cap C[a,b]$ occurs only in the case
$$ BV[a, b] \cap C[a,b] = F^{1/\varepsilon}, $$
where
$BV[a,b]$ are functions of classical bounded variation. For other cases, a counterexample is constructed showing that if
$\mu(\varepsilon)$ grows faster than
$\dfrac{1}{\varepsilon}$ as
$\varepsilon \to +0$, then the class
$F^{\mu} $ is not a subclass of any of the classes
$BV_{\Phi}[a, b]$.
Keywords:
fractal dimension, bounded variation.
UDC:
517.518.2
MSC: 26A45,
26A99 Received: 17.03.2023
Revised: 20.10.2023
Accepted: 23.10.2023
DOI:
10.21538/0134-4889-2023-29-4-155-168