Further quantitative moduli around uniform convexity
We derive new formulas for quantities involved in the study of uniformly convex spaces, linear and nonlinear.
math.FA↗
arXiv subjects
Andrei Sipos
Publications and source records attributed to Andrei Sipos.
On the uniform convexity of the squared distance
In 1983, Z\u{a}linescu showed that the squared norm of a uniformly convex normed space is uniformly convex on bounded subsets. We extend this result to the metric setting of uniformly convex hyperbolic spaces. We derive applications to the convergence of shadow sequences and to proximal minimization.
math.MG↗
Products of hyperbolic spaces
The class of uniformly smooth hyperbolic spaces was recently introduced by the first author as a common generalization of both CAT(0) spaces and uniformly smooth Banach spaces, in a way that Reich's theorem on resolvent convergence could still be proven. We define products of such spaces, showing that they are reasonably well-behaved. In this manner, we provide the first example of a space for which Reich's theorem holds and which is neither a CAT(0) space, nor a convex subset of a normed space.
math.MG↗
Normal forms and representable functions in Moisil logic
In this note, we determine, by a disjunctive normal form theorem, which functions on the standard $n$-nuanced \L ukasiewicz-Moisil algebra are representable by formulas and we show how this result may help in establishing the structure of the free algebras in this class.
math.LO↗
The computational content of super strongly nonexpansive mappings and uniformly monotone operators
Recently, Liu, Moursi and Vanderwerff have introduced the class of super strongly nonexpansive mappings as a counterpart to operators which are maximally monotone and uniformly monotone. We give a quantitative study of these notions in the style of proof mining, providing a modulus of super strong nonexpansiveness, giving concrete examples of it and connecting it to moduli associated to uniform monotonicity. For the supercoercive case, we analyze the situation further, yielding a quantitative inconsistent feasibility result for this class (obtaining effective uniform rates of asymptotic regularity), a result which is also qualitatively new.
math.OC↗
On quantitative metastability for accretive operators
Kohlenbach and the author have extracted a rate of metastability for approximate curves associated to continuous pseudocontractive self-mappings in Banach spaces which are uniformly convex and uniformly smooth, whose convergence is due to Reich. In this note, we show that this result may be extended to Reich's original convergence statement involving resolvents of accretive operators.
math.FA↗
A proof-theoretic metatheorem for tracial von Neumann algebras
We adapt a continuous logic axiomatization of tracial von Neumann algebras due to Farah, Hart and Sherman in order to prove a metatheorem for this class of structures in the style of proof mining, a research program that aims to obtain the hidden computational content of ordinary mathematical proofs using tools from proof theory.
math.LO↗
Hilbert space representation of binary operations on a power-multiplying oscillator
In this study, the properties of an oscillating system composed of a pendulum connected to a seesaw and placed on a moving platform with a certain slope are analyzed. Using complex numbers to collect the information contained in the system proves to be crucial in order to observe the properties described by both cross and dot products. The representation of physical quantities in complex numbers reveals that for certain angles, precisely those where the oscillation translates into a displacement, the properties of the system are expressed in the real plane.
physics.class-ph↗
Bounds on strong unicity for Chebyshev approximation with bounded coefficients
We obtain new effective results in best approximation theory, specifically moduli of uniqueness and constants of strong unicity, for the problem of best uniform approximation with bounded coefficients, as first considered by Roulier and Taylor. We make use of techniques from the field of proof mining, as introduced by Kohlenbach in the 1990s. In addition, some bounds are obtained via the Lagrangian interpolation formula as extended through the use of Schur polynomials to cover the case when certain coefficients are restricted to be zero.
math.CA↗
Two-dimensional array for operating an oscillator in Euclidean space $\mathbb{R}^3$, as a power multiplier
In the present study an oscillator system formed by a seesaw connected to a simple pendulum coupled to a mobile platform with a certain slope, is analyzed. The observed properties of the system when faced with a possible displacement of the mobile are affected in terms of energy loss, which can be reflected in the angle, the variation of apparent weight and the height. The possible variations which can be introduced modify these parameters, so that the system tries to compensate them in order to preserve its symmetry. The working of this system can be described by means of a transformation matrix where the nature of the movement is represented. Such tool enables us to observe the variations that the system may experience as rotation and translation functions. Therefore, the matrix offers a clear visualization of the values expressed and thus of the need to either provide or extract energy to or from the system.
physics.class-ph↗
Energy implications of a load depending on geometrical configurations in an oscillator
This paper studies, for a specific oscillatory system composed by a pendulum connected to a seesaw, how the geometry of the different mechanisms of energy introduction conditions the resulting movement, to achieve both a greater amplitude of oscillation due to a change of velocity and an acceleration in its movement. The different configurations that give rise to the acceleration of motion are therefore analyzed. The study is carried out from a kinematic point of view, theoretically simulating an energy increase in the system and analyzing its response in terms of angular velocity and of modification of apparent weight. Subsequently, the force diagram necessary to generate the accelerated motion is analyzed. The magnitude of the external force to be applied and its dependence on the direction and angular instant in which it are exerted is evaluated. It is observed how for some specific configurations this magnitude is negative, implying that the system is capable of accelerating when subjected to a brake or load on it.
physics.class-ph↗
On extracting variable Herbrand disjunctions
Some quantitative results obtained by proof mining take the form of Herbrand disjunctions that may depend on additional parameters. We attempt to elucidate this fact through an extension to first-order arithmetic of the proof of Herbrand's theorem due to Gerhardy and Kohlenbach which uses the functional interpretation.
math.LO↗
A quantitative multiparameter mean ergodic theorem
We use techniques of proof mining to obtain a computable and uniform rate of metastability (in the sense of Tao) for the mean ergodic theorem for a finite number of commuting linear contractive operators on a uniformly convex Banach space.
math.DS↗
Abstract strongly convergent variants of the proximal point algorithm
We prove an abstract form of the strong convergence of the Halpern-type and Tikhonov-type proximal point algorithms in CAT(0) spaces. In addition, we derive uniform and computable rates of metastability (in the sense of Tao) for these iterations using proof mining techniques.
math.OC↗
Construction of fixed points of asymptotically nonexpansive mappings in uniformly convex hyperbolic spaces
Kohlenbach and Leustean have shown in 2010 that any asymptotically nonexpansive self-mapping of a bounded nonempty $UCW$-hyperbolic space has a fixed point. In this paper, we adapt a construction due to Moloney in order to provide a sequence that converges strongly to such a fixed point.
math.MG↗
Rates of metastability for iterations on the unit interval
We use techniques of proof mining to extract computable and uniform rates of metastability (in the sense of Tao) for iterations of continuous functions on the unit interval, firstly (following earlier work of Gaspar) out of convergence proofs due to Franks, Marzec, Rhoades and Hillam and then out of an argument due to Borwein and Borwein that pertains only to Lipschitz functions.
math.CA↗
Revisiting jointly firmly nonexpansive families of mappings
Recently, the author, together with L. Leustean and A. Nicolae, introduced the notion of jointly firmly nonexpansive families of mappings in order to investigate in an abstract manner the convergence of proximal methods. Here, we further the study of this concept, by giving a characterization in terms of the classical resolvent identity, by improving on the rate of convergence previously obtained for the uniform case, and by giving a treatment of the asymptotic behaviour at infinity of such families.
math.OC↗
The finitary content of sunny nonexpansive retractions
We use techniques of proof mining to extract a uniform rate of metastability (in the sense of Tao) for the strong convergence of approximants to fixed points of uniformly continuous pseudocontractive mappings in Banach spaces which are uniformly convex and uniformly smooth, i.e. a slightly restricted form of the classical result of Reich. This is made possible by the existence of a modulus of uniqueness specific to uniformly convex Banach spaces and by the arithmetization of the use of the limit superior. The metastable convergence can thus be proved in a system which has the same provably total functions as first-order arithmetic and therefore one may interpret the resulting proof in Gödel's system $T$ of higher-type functionals. The witness so obtained is then majorized (in the sense of Howard) in order to produce the final bound, which is shown to be definable in the subsystem $T_1$. This piece of information is further used to obtain rates of metastability to results which were previously only analyzed from the point of view of proof mining in the context of Hilbert spaces, i.e. the convergence of the iterative schemas of Halpern and Bruck.
math.FA↗