
An increasing continuous function \(f:\mathbb{R}^+\to\mathbb{R}^+\) is called a modulus function if \(f(0)=0\), \(f(t) > 0\) for \(t > 0\), and \(f(t+s)\leq f(t)+f(s)\) for every \(t,s \in \mathbb{R}^+\). Let \(f\) be an unbounded modulus function. A sequence \((x_n)\) in a normed space \(X\) is said to be \(f\)-statistically convergent to \(x \in X\) if, for every \(\varepsilon > 0\), \[ \lim_{n\to \infty} \frac{f(|\{k \in \mathbb N: k \leq n \, \mathrm{ and } \, \|x_k - x\| > \varepsilon\}|)}{f(n)} = 0. \] For \(f(t) = t\), the corresponding \(f\)-statistical convergence coincides with the ordinary statistical convergence widely studied in past decades. Statistical and \(f\)-statistical convergences are particular cases of filter convergence or, in other terminology, of ideal convergence. The author proves that for a normed space \(X\) its completeness with respect to \(f\)-statistical convergence is equivalent to the usual completeness. Relation of weak \(f\)-statistical convergence with weak convergence on a subset of maximal \(f\)-density is studied. The last subsection is devoted to \(f\)-statistical cluster points.
46A45, normed space, statistical convergence, cluster points, Summability in abstract structures, moduli, Ideal and statistical convergence, 40A35
46A45, normed space, statistical convergence, cluster points, Summability in abstract structures, moduli, Ideal and statistical convergence, 40A35
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