2
$\begingroup$

This is a follow up to this question, which was answered in the affirmative: Are continuous functions almost completely determined by their modulus of continuity?

Note: We do not identify functions that agree a.e.

Given $f: R \to R$ in $L^{1}_{loc}$, define the approximate left modulus of continuity, $L_f (x, e): \mathbb R \times \mathbb R^+ \to [0, \infty]$ by

$$L_{f} (x, e)=\sup \{ d \geq 0\: \big|\, A(f, r) \leq e, \forall r \text{ s.t. } 0 \leq r \leq d \}.$$

where $A(f, r) := \frac{1}{r} \int\limits_{[x-r, x]} |f(t) - f(x)| {d}t.$

Similarly define the approximate right modulus of continuity by

$$R_{f} (x, e)=\sup \{ d \geq 0\: \big| I(f, r) \leq e, \forall r \text{ s.t } 0 \leq r \leq d \}.$$

where $I(f, r) := \frac{1}{r} \int\limits_{[x, x + r]} |f(t) - f(x)| {d}t.$

Note that if $f = g$ a.e., then $L_f = L_g$ a.e. and $R_f = R_g$ a.e., by which we mean for almost all $x$, for all $e$, $L_f (x, e) = R_f (x, e).$

Do $L_f$ and $R_f$ almost determine f uniquely? In the following sense:

Suppose $f$ and $g$ in $L^{1}_{loc}$ are such that $L_f = L_g$ a.e. and $R_f = R_g$ a.e. Does it follow that $f = g + c$ a.e. or $f = -g + c$ a.e. for some a.e. constant function $c$?

$\endgroup$

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.