Positive operators and Hausdorff dimension of invariant sets

• Published in: Transactions of the American Mathematical Society 2012-02, Vol.364 (2), p.1029-1066
• Main Authors: NUSSBAUM, ROGER D., PRIYADARSHI, AMIT, LUNEL, SJOERD VERDUYN
• Format: Article
• Language: English
• Subjects: Banach space; Eigenvalues; Eigenvectors; Hausdorff dimensions; Integers; Iterations of functions; Linear transformations; Mathematical theorems; Mathematics; Spectral theory
• ISSN: 0002-9947; 1088-6850
• DOI: 10.1090/S0002-9947-2011-05484-X

In this paper we obtain theorems which give the Hausdorff dimension of the invariant set for a finite family of contraction mappings which are ``infinitesimal similitudes'' on a complete, perfect metric space. Our work generalizes the graph-directed construction of Mauldin and Williams (1988) and is related in its general setting to results of Schief (1996), but differs crucially in that the mappings need not be similitudes. We use the theory of positive linear operators and generalizations of the Krein-Rutman theorem to characterize the Hausdorff dimension as the unique value of \sigma > 0 r(L_\sigma )=1, \sigma >0 r(L_\sigma ). We also indicate how these results can be generalized to countable families of infinitesimal similitudes. The intent here is foundational: to derive a basic formula in its proper generality and to emphasize the utility of the theory of positive linear operators in this setting. Later work will explore the usefulness of the basic theorem and its functional analytic setting in studying questions about Hausdorff dimension.