Abstract
Let \(({{x}_{n}})\) be a sequence and \(\rho \geqslant 1\) . For two fixed sequences \({{n}_{1}} < {{n}_{2}} < {{n}_{3}} < \ldots \) , and \(M\) define the oscillation operator \({{\mathcal{O}}_{\rho }}({{x}_{n}}) = {{\left( {\sum\limits_{k = 1}^\infty \,\mathop {\sup }\limits_{\substack{ {{n}_{k}} \leqslant m < {{n}_{{k + 1}}} \\ m \in M } } {{{\left| {{{x}_{m}} - {{x}_{{{{n}_{k}}}}}} \right|}}^{\rho }}} \right)}^{{1/\rho }}}.\) Let \((X,\mathcal{B},\mu ,\tau )\) be a dynamical system with \((X,\mathcal{B},\mu )\) a probability space and \(\tau \) a measurable, invertible, measure preserving point transformation from \(X\) to itself. Suppose that the sequences \(({{n}_{k}})\) is a lacunary, and \(M\) is any sequence of positive real numbers such that there exists an \(\ell \in \mathbb{R}\) satisfying \(\# \{ m \in M:{{n}_{k}} \leqslant m < {{n}_{{k + 1}}}\} \leqslant \ell \) for all \(k \in \mathbb{N}\) to obtain the above mentioned results, where \(\# \) denotes cardinality. Then we prove the following results for \(\rho \geqslant 2\) : (i) Define \({{\phi }_{n}}(x) = \frac{1}{n}{{\chi }_{{[0,n]}}}(x)\) on \(\mathbb{R}\) . Then there exists a constant \(C > 0\) such that \({{\left\| {{{\mathcal{O}}_{\rho }}({{\phi }_{n}} * f)} \right\|}_{{{{L}^{1}}(\mathbb{R})}}} \leqslant C{{\left\| f \right\|}_{{{{H}^{1}}(\mathbb{R})}}}\) for all \(f \in {{H}^{1}}(\mathbb{R})\) .(ii) Let \({{A}_{n}}f(x) = \frac{1}{n}\sum\limits_{k = 1}^n \,f({{\tau }^{k}}x)\) be the usual ergodic averages in ergodic theory. Then \({{\left\| {{{\mathcal{O}}_{\rho }}({{A}_{n}}f)} \right\|}_{{{{L}^{1}}(X)}}} \leqslant C{{\left\| f \right\|}_{{{{H}^{1}}(X)}}}\) for all \(f \in {{H}^{1}}(X)\) . (iii) If \({{[f(x)\log (x)]}^{ + }}\) is integrable, then \({{\mathcal{O}}_{\rho }}({{A}_{n}}f)\) is integrable. In the author’s previously published article titled “Oscillation inequalities on real and ergodic \({{H}^{1}}\) spaces” the above results have been obtained when both \(({{n}_{k}})\) and \(M\) are lacunary. Thus the results of this work extents those results to a nonlacunary sequence \(M\) with a more general growth condition.