Parametrization, Embedding and Extension Problems in Metric Spaces

几何函数理论是20世纪20年代为了从几何角度研究解析函数而发展起来的一个数学领域，后来发展到今天所知的度量空间分析。几何方法的优点是，一阶微分和几何测量理论可以从经典的欧几里得或黎曼设置扩展到没有先验光滑结构的空间领域（如分形空间）。近年来，几何函数理论的成果和技术在几何群论、流形结构和分形分析中得到了重要的应用。此外，除了数学上的重要性外，这些理论的物理应用还包括重建理论、薄膜研究、控制理论、图形成像和大数据集分析。该项目以解决几何函数理论领域中三个长期存在的问题为特色，汇集了分析和几何的几个领域，包括几何拓扑、亚黎曼几何、PL几何和几何测量理论。第一个问题旨在识别度量空间的内在性质，从中可以恢复欧几里得单位球或欧几里得空间的“好”参数化（例如准对称，Holder, bi-Lipschitz）。主要研究者建议将离散曲率的形式与高维的全局参数化联系起来。第二个问题问的是一个集合嵌入欧几里德空间的条件，该空间具有某些期望的性质（如拟对称，双lipschitz），可以扩展到具有相同性质的整个欧几里德空间。最后，第三个问题涉及子黎曼流形的大集合（如海森堡群）在欧几里德空间中的双lipschitz嵌入性。在这个方向上的结果将为空间的结构提供新的亮点，并将提高我们对其几何形状的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Geometric function theory is a field of mathematics that was developed starting in the 1920s in order to study analytic functions from a geometric point of view, and was later developed to what is known today as analysis of metric spaces. The advantage of a geometric approach, is that first order differential calculus and geometric measure theory can be extended from the classical Euclidean or Riemannian settings to the realm of spaces without a priori smooth structure (such as fractal spaces). Results and techniques in geometric function theory have recently found important applications in geometric group theory, structure of manifolds and analysis on fractals. Furthermore, besides their mathematical importance, physical applications of these theories include reconstruction theory, study of thin films, control theory, graphic imaging and analysis of large data sets.This project features new approaches to three long-standing problems in the realm of geometric function theory that bring together several fields in analysis and geometry including geometric topology, sub-Riemannian geometry, PL geometry and geometric measure theory. The first problem aims at recognizing the intrinsic qualities of a metric space, from which a "nice" parametrization (e.g. quasisymmetric, Holder, bi-Lipschitz) by the Euclidean unit sphere or the Euclidean space can be recovered. The principal investigator proposes to relate forms of discrete curvature with global parametrizations in high dimensions. The second problem asks for conditions for which an embedding of a set into a Euclidean space with some desired properties (e.g. quasisymmetric, bi-Lipschitz) can be extended to the whole Euclidean space with the same properties. Finally, the third problem concerns the bi-Lipschitz embedability of big sets of a sub-Riemannian manifolds (such as the Heisenberg group) into some Euclidean space. Results in this direction will shed new light on the structure of the space and will improve our understanding of its geometry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.