
Let Ψ \Psi be a convex function, and let f be a real-valued function on [0, 1]. Let a modulus of continuity associated to Ψ \Psi be given as \[ Q Ψ ( δ , f ) = inf { λ : 1 δ ∬ | x − y | ⩽ δ Ψ ( | f ( x ) − f ( y ) | λ ) d x d y ⩽ Ψ ( 1 ) } . {Q_\Psi }(\delta ,f) = \inf \left \{ {\lambda :\frac {1}{\delta }\iint \limits _{|x - y| \leqslant \delta } {\Psi \left ( {\frac {{|f(x) - f(y)|}}{\lambda }} \right )}\;dx\;dy\; \leqslant \Psi (1)} \right \}. \] It is shown that ∫ 0 1 Q Ψ ( δ , f ) d ( − Ψ − 1 ( c / δ ) ) > ∞ \smallint _0^1{Q_\Psi }(\delta ,f)\;d\;( - {\Psi ^{ - 1}}(c/\delta )) > \infty guarantees the essential continuity of f, and, in fact, a uniform Lipschitz estimate is given. In the case that Ψ ( u ) = exp u 2 \Psi (u) = \exp \;{u^2} the above condition reduces to \[ ∫ 0 1 Q exp u 2 ( δ , f ) d δ δ log ( c / δ ) > ∞ . \int _0^1 {{Q_{\exp \;{u^2}}}\;(\delta ,f)\frac {{d\delta }}{{\delta \sqrt {\log (c/\delta )} }}\; > \infty .} \] This exponential square condition is satisfied almost surely by the random Fourier series f t ( x ) = Σ n = 1 ∞ a n R n ( t ) e i n x {f_t}(x) = \Sigma _{n = 1}^\infty {a_n}{R_n}(t){e^{inx}} , where { R n } \{ {R_n}\} is the Rademacher system, as long as \[ ∫ 0 1 a n 2 sin 2 ( n δ / 2 ) d δ δ log ( 1 / δ ) > ∞ . \int _0^1 {\sqrt {a_n^2{{\sin }^2}(n\delta /2)} \frac {{d\delta }}{{\delta \sqrt {\log (1/\delta )} }}\; > \infty .} \] Hence, the random essential continuity of f t ( x ) {f_t}(x) is guaranteed by each of the above conditions.
Continuity and related questions (modulus of continuity, semicontinuity, discontinuities, etc.) for real functions in one variable, Convexity of real functions in one variable, generalizations, Probabilistic methods for one variable harmonic analysis
Continuity and related questions (modulus of continuity, semicontinuity, discontinuities, etc.) for real functions in one variable, Convexity of real functions in one variable, generalizations, Probabilistic methods for one variable harmonic analysis
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