5,163 research outputs found
The twistor discriminant locus of the Fermat cubic
We consider the discriminant locus of the Fermat cubic under the twistor
fibration . We show that it has a conformal symmetry
group of order and use this to identify its topology.Comment: 30 pages, 4 figure
The thick-thin decomposition and the bilipschitz classification of normal surface singularities
We describe a natural decomposition of a normal complex surface singularity
into its "thick" and "thin" parts. The former is essentially metrically
conical, while the latter shrinks rapidly in thickness as it approaches the
origin. The thin part is empty if and only if the singularity is metrically
conical; the link of the singularity is then Seifert fibered. In general the
thin part will not be empty, in which case it always carries essential
topology. Our decomposition has some analogy with the Margulis thick-thin
decomposition for a negatively curved manifold. However, the geometric behavior
is very different; for example, often most of the topology of a normal surface
singularity is concentrated in the thin parts.
By refining the thick-thin decomposition, we then give a complete description
of the intrinsic bilipschitz geometry of in terms of its topology and a
finite list of numerical bilipschitz invariants.Comment: Minor corrections. To appear in Acta Mathematic
Nearest Points on Toric Varieties
We determine the Euclidean distance degree of a projective toric variety.
This extends the formula of Matsui and Takeuchi for the degree of the
-discriminant in terms of Euler obstructions. Our primary goal is the
development of reliable algorithmic tools for computing the points on a real
toric variety that are closest to a given data point.Comment: 20 page
Lipschitz geometry of complex surfaces: analytic invariants and equisingularity
We prove that the outer Lipschitz geometry of a germ of a normal
complex surface singularity determines a large amount of its analytic
structure. In particular, it follows that any analytic family of normal surface
singularities with constant Lipschitz geometry is Zariski equisingular. We also
prove a strong converse for families of normal complex hypersurface
singularities in : Zariski equisingularity implies Lipschitz
triviality. So for such a family Lipschitz triviality, constant Lipschitz
geometry and Zariski equisingularity are equivalent to each other.Comment: Added a new section 10 to correct a minor gap and simplify some
argument
Minimal surface singularities are Lipschitz normally embedded
Any germ of a complex analytic space is equipped with two natural metrics:
the {\it outer metric} induced by the hermitian metric of the ambient space and
the {\it inner metric}, which is the associated riemannian metric on the germ.
We show that minimal surface singularities are Lipschitz normally embedded
(LNE), i.e., the identity map is a bilipschitz homeomorphism between outer and
inner metrics, and that they are the only rational surface singularities with
this property.Comment: This paper is a major revision of the 2015 version. It now builds on
the paper arXiv:1806.11240 by the same authors which gives a general
characterization of Lipschitz normally embedded surface singularitie
The Euclidean distance degree of an algebraic variety
The nearest point map of a real algebraic variety with respect to Euclidean
distance is an algebraic function. For instance, for varieties of low rank
matrices, the Eckart-Young Theorem states that this map is given by the
singular value decomposition. This article develops a theory of such nearest
point maps from the perspective of computational algebraic geometry. The
Euclidean distance degree of a variety is the number of critical points of the
squared distance to a generic point outside the variety. Focusing on varieties
seen in applications, we present numerous tools for exact computations.Comment: to appear in Foundations of Computational Mathematic
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