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Olga Maleva

Publications and source records attributed to Olga Maleva.

11 recordsLinked to original sources
arXiv2025

Chain rule for pointwise Lipschitz mappings

The classical Chain Rule formula $(f\circ g)'(x;u)=f'(g(x);g'(x;u))$ gives the (partial, or directional) derivative of the composition of mappings $f$ and $g$. We show how to get rid of the unnecessarily strong assumption of differentiability at all of the relevant points: the mappings do not need to be defined on the whole space and it is enough for them to be pointwise Lipschitz. The price to pay is that the Chain Rule holds almost everywhere. We extend this construction to infinite-dimensional spaces with good properties (Banach, separable, Radon-Nikod\'ym) with an appropriate notion of almost everywhere. Pointwise Lipschitzness is a local condition in contrast to the global Lipschitz property: we do not need the mappings to be defined on the whole space, or even locally in a neighbourhood, nor to know their behaviour far away from the points we consider. This distinguishes our results from recent research on the differentiation of the composition of Lipschitz mappings. The methods we develop for the purpose of proving the Chain Rule also allow us to strengthen the Rademacher-Stepanov type theorem on almost everywhere differentiability of a mapping.

math.FA↗
arXiv2025

Extreme non-differentiability of typical Lipschitz mappings

We show that no matter what subset of a normed space is given, a typical 1-Lipschitz mapping into a Banach space is non-differentiable at a typical point of the set in a very strong sense: the derivative ratio approximates, on arbitrary small scales, every linear operator of norm at most 1. For subsets of finite-dimensional normed spaces which can be covered by a countable union of closed purely unrectifiable sets this extreme non-differentiability holds for a typical Lipschitz mapping at every point. Both results are new even for Lipschitz mappings with a finite-dimensional co-domain.

math.FA↗
arXiv2023

On the structural decomposition of planar Lipschitz quotient mappings

We show that for each fixed non-constant complex polynomial $P$ of the plane there exists a homeomorphism $h$ such that $P\circ h$ is a Lipschitz quotient mapping. This corrects errors in the construction given earlier by Johnson et. al. [Michigan Math. J. $\textbf{47}$ (2000), 15-31]. Further we introduce a stronger notion of pointwise co-Lipschitzness and characterise its equivalence to the standard pointwise definition whilst also highlighting its relevance to a long-standing conjecture concerning Lipschitz quotient mappings $\mathbb{R}^n\to\mathbb{R}^n, n\geq 3$.

math.FA↗
arXiv2021

Typical Lipschitz mappings are typically non-differentiable

We prove that a typical Lipschitz mapping between any two Banach spaces is non-differentiable at typical points of any given subset of its domain in the most extreme form. This is a new result even for Lipschitz mappings between Euclidean spaces.

math.FA↗
arXiv2020

A dichotomy of sets via typical differentiability

We obtain a criterion for an analytic subset of a Euclidean space to contain points of differentiability of a typical Lipschitz function, namely, that it cannot be covered by countably many sets, each of which is closed and purely unrectifiable (has zero length intersection with every $C^1$ curve). Surprisingly, we establish that any set failing this criterion witnesses the opposite extreme of typical behaviour: In any such coverable set a typical Lipschitz function is everywhere severely non-differentiable.

math.FA↗
arXiv2017

Cone unrectifiable sets and non-differentiability of Lipschitz functions

We provide sufficient conditions for a set $E\subset\mathbb{R}^n$ to be a non-universal differentiability set, i.e. to be contained in the set of points of non-differentiability of a real-valued Lipschitz function. These conditions are motivated by a description of the ideal generated by sets of non-differentiability of Lipschitz self-maps of $\mathbb{R}^n$ given by Alberti, Csörnyei and Preiss, which eventually led to the result of Jones and Csörnyei that for every Lebesgue null set $E$ in $\mathbb{R}^n$ there is a Lipschitz map $f:\mathbb{R}^n\to\mathbb{R}^n$ not differentiable at any point of $E$, even though for $n>1$ and for Lipschitz functions from $\mathbb{R}^n$ to $\mathbb{R}$ there exist Lebesgue null universal differentiability sets.

math.FA↗
arXiv2013

Differentiability inside sets with upper Minkowski dimension one

We show that every finite-dimensional Euclidean space contains compact universal differentiability sets of upper Minkowski dimension one. In other words, there are compact sets $S$ of upper Minkowski dimension one such that every Lipschitz function defined on the whole space is differentiable inside $S$. Such sets are constructed explicitly.

math.FA↗
arXiv2006

Metric derived numbers and continuous metric differentiability via homeomorphisms

We define the notions of unilateral metric derivatives and ``metric derived numbers'' in analogy with Dini derivatives (also referred to as ``derived numbers'') and establish their basic properties. We also prove that the set of points where a path with values in a metric space with continuous metric derivative is not ``metrically differentiable'' (in a certain strong sense) is $σ$-symmetrically porous and provide an example of a path for which this set is uncountable. In the second part of this paper, we study the continuous metric differentiability via a homeomorphic change of variable.

math.CA↗