We say a measure is @math @math -rectifiable if there is a countable union of @math @math -surfaces whose complement has measure zero. We provide sufficient conditions for a Radon measure in @math to be @math @math -rectifiable, with @math . We assume a priori the measure to have positive and finite upper density. The conditions involve a Bishop-Jones type square function and all statements are quantitative in that the @math constants depend on such a function. Along the way we also give sufficient conditions for @math parametrizations for one-sided Reifenberg flat sets in terms of the same square function. Key tools for the proof come from Guy David and Tatiana Toro's Reifenberg parametrizations of sets with holes in the Holder and Lipschitz categories.
In the last few years, C. Fefferman, A. Israel, and G.K. Luli @cite_52 have been investigating Whitney type extension problems for @math maps, finding conditions to fit smooth functions to data.
@cite_52
2038964811
In the 0-extension problem, we are given a weighted graph with some nodes marked as terminals and a semimetric on the set of terminals. Our goal is to assign the rest of the nodes to terminals so as to minimize the sum, over all edges, of the product of the edge's weight and the distance between the terminals to which its endpoints are assigned. This problem generalizes the multiway cut problem of [SIAM J. Comput. , 23 (1994), pp. 864--894] and is closely related to the metric labeling problem introduced by Kleinberg and Tardos [Proceedings of the 40th IEEE Annual Symposium on Foundations of Computer Science, New York, 1999, pp. 14--23]. We present approximation algorithms for 0-Extension . In arbitrary graphs, we present a O(log k)-approximation algorithm, k being the number of terminals. We also give O(1)-approximation guarantees for weighted planar graphs. Our results are based on a natural metric relaxation of the problem previously considered by Karzanov [European J. Combin., 19 (1998), pp. 71--101]. It is similar in flavor to the linear programming relaxation of Garg, Vazirani, and Yannakakis [SIAM J. Comput. , 25 (1996), pp. 235--251] for the multicut problem, and similar to relaxations for other graph partitioning problems. We prove that the integrality ratio of the metric relaxation is at least @math for a positive c for infinitely many k. Our results improve some of the results of Kleinberg and Tardos, and they further our understanding on how to use metric relaxations.