arXiv subjects

J. D. Meiss

Publications and source records attributed to J. D. Meiss.

At least 19 recordsLinked to original sources

arXiv2025

Recurrence and Stickiness in the Noisy Harper Map

When three types of noise are introduced to the area-preserving Harper map, the Poincaré recurrence statistic (PRS) exhibits an extended tail, corresponding to an increased probability of longer recurrence times. For a deterministic case with a mixture of regular and chaotic orbits, regular islands are responsible for a power-law decay in the recurrence distribution. Noise perturbations allow trajectories to access the interior of the islands, and this can enhance their trapping effect, causing many orbits to take longer to return to a neighborhood of their initial conditions and resulting in a slower power-law decay on an intermediate time scale. On a longer time scale, however, the noisy PRS exhibits exponential decay, eventually falling below the deterministic PRS. We compare distributions of trapping and visit times to islands with recurrence times to show the importance of noise in creating tails in the PRS. A simple model of the dynamics -- a Markov chain with three states -- demonstrates how the slower decay can be caused by noise allowing entry to a previously inaccessible island.

nlin.CD↗

arXiv2025

Hamiltonian Triplet Interactions: Areal and Perimetric Forces

Gravitational and electromagnetic interactions are Hamiltonian systems with forces between pairs of particles. We propose an alternative: Hamiltonian dynamics with triplet interactions between point particles. Our system has a potential energy that depends on the shape of the triangle for each triplet. Similar multi-body forces occur in many physical systems, e.g., polarizable molecules, nucleon interactions, and colloids, but typically are combined with more conventional two-body forces. We focus on potentials that depend only on the triangle perimeter or on its area. The resulting forces point towards a center of the triangle, either the incenter or the orthocenter, respectively. For the planar case, the resulting system has six degrees of freedom but can be reduced to three since it conserves the total momentum and angular momentum. The dynamics often exhibits chaotic motion, but there are a number of special solutions, for example equilateral and isosceles triangles, and perturbations of these can lie on invariant tori. Numerical investigations of several examples show families of such regular trajectories as well as examples of chaotic dynamics.

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arXiv2024

Computing Lyapunov Exponents using Weighted Birkhoff Averages

The Lyapunov exponents of a dynamical system measure the average rate of exponential stretching along an orbit. Positive exponents are often taken as a defining characteristic of chaotic dynamics. However, the standard orthogonalization-based method for computing Lyapunov exponents converges slowly -- if at all. Many alternatively techniques have been developed to distinguish between regular and chaotic orbits, though most do not compute the exponents. We compute the Lyapunov spectrum in three ways: the standard method, the weighted Birkhoff average (WBA), and the ``mean exponential growth rate for nearby orbits'' (MEGNO). The latter two improve convergence for nonchaotic orbits, but the WBA is fastest. However, for chaotic orbits the three methods convergence at similar, slow rates. Though the original MEGNO method does not compute Lyapunov exponents, we show how to reformulate it as a weighted average that does.

nlin.CD↗

arXiv2024

Resonance and Weak Chaos in Quasiperiodically-Forced Circle Maps

In this paper, we focus on a numerical technique, the weighted Birkhoff average (WBA) to distinguish between four categories of dynamics for quasiperiodically-forced circle maps. Regular dynamics can be classified by rotation vectors, and these can be rapidly computed to machine precision using the WBA. Regular orbits can be resonant or incommensurate and we distinguish between these by computing their "resonance order." When the dynamics is chaotic the WBA converges slowly. Such orbits can be strongly chaotic, when they have a positive Lyapunov exponent or weakly chaotic, when the maximal Lyapunov exponent is zero. The latter correspond to the strange nonchaotic attractors (SNA) that have been observed in quasiperiodically-forced circle maps beginning with the models introduced by Ding, Grebogi, and Ott. The WBA provides a new technique to find SNAs, and allows us to accurately compute the proportions of each of the four orbit types as a function of map parameters.

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arXiv2024

Proportions of Incommensurate, Resonant, and Chaotic Orbits for Torus Maps

This paper focuses on distinguishing classes of dynamical behavior for one- and two-dimensional torus maps, in particular between orbits that are incommensurate, resonant, periodic, or chaotic. We first consider Arnold's circle map, for which there is a universal power law for the fraction of nonresonant orbits as a function of the amplitude of the nonlinearity. Our methods give a more precise calculation of the coefficients for this power law. For two-dimensional torus maps, we show that there is no such universal law for any of the classes of orbits. However, we find different categories of maps with qualitatively similar behavior. Our results are obtained using three fast and high precision numerical methods: weighted Birkhoff averages, Farey trees, and resonance orders.

math.DS↗

arXiv2023

Symmetry Reduction and Rotation Numbers for Poncelet maps

Poncelet maps are circle maps constructed geometrically for a pair of nested ellipses; they are related to the classic billiard map on an elliptical domain when the orbit has an elliptical caustic. Here we show how the rotation number of the elliptical billiard map can be obtained from a symmetry generated from the flow of a pendulum Hamiltonian system. When such a symmetry flow has a global cross section, we previously showed that there are coordinates in which the map takes a reduced, skew-product form on a covering space. In particular, for elliptic billiard map this gives an explicit form for the rotation number of each orbit. We show that the family Poncelet maps on a pencil of ellipses is conjugate to a corresponding family of billiard maps, and thus the Poncelet maps inherit the one-parameter family of continuous symmetries. Such a pencil has a single parameter, the pencil eccentricity, which becomes the modulus of the Jacobi elliptic functions used to construct a covering space that simultaneously simplifies all of the Poncelet maps. The rotation number of the Poncelet map for any element of a pencil can then be written in terms of elliptic functions as well. An implication is that the rotation number of the pencil has a monotonicity property: it is monotone increasing as the caustic ellipse shrinks. The resulting expression for the rotation number gives an explicit condition for Poncelet porisms, the parameters for which the rotation number is rational. For such parameters, an orbit of the corresponding Poncelet map is periodic: it forms a polygon for any initial point. These universal parameters also solve the inverse problem: given a rotation number, which member of a pencil has a Poncelet map with that rotation number? Explicit conditions are given for a general rotation numbers and we see how they are related to Cayley's classic porism theorem.

math.DS↗

arXiv2021

Birkhoff Averages and the Breakdown of Invariant Tori in Volume-Preserving Maps

In this paper, we develop numerical methods based on the weighted Birkhoff average for studying two-dimensional invariant tori for volume-preserving maps. The methods do not rely on symmetries, such as time-reversal symmetry, nor on approximating tori by periodic orbits. The rate of convergence of the average gives a sharp distinction between chaotic and regular dynamics and allows accurate computation of rotation vectors for regular orbits. Resonant and rotational tori are distinguished by computing the resonance order of the rotation vector to a given precision. Critical parameter values, where tori are destroyed, are computed by a sharp decrease in convergence rate of the Birkhoff average. We apply these methods for a three-dimensional generalization of Chirikov's standard map: an angle-action map with two angle variables. Computations on grids in frequency and perturbation amplitude allow estimates of the critical set. We also use continuation to follow tori with fixed rotation vectors. We test three conjectures for cubic fields that have been proposed to give locally robust invariant tori.

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arXiv2020

Leveraging the Mathematics of Shape for Solar Magnetic Eruption Prediction

Current operational forecasts of solar eruptions are made by human experts using a combination of qualitative shape-based classification systems and historical data about flaring frequencies. In the past decade, there has been a great deal of interest in crafting machine-learning (ML) flare-prediction methods to extract underlying patterns from a training set---e.g., a set of solar magnetogram images, each characterized by features derived from the magnetic field and labeled as to whether it was an eruption precursor. These patterns, captured by various methods (neural nets, support vector machines, etc.), can then be used to classify new images. A major challenge with any ML method is the \textit{featurization} of the data: pre-processing the raw images to extract higher-level properties, such as characteristics of the magnetic field, that can streamline the training and use of these methods. It is key to choose features that are informative, from the standpoint of the task at hand. To date, the majority of ML-based solar eruption methods have used physics-based magnetic and electric field features such as the total unsigned magnetic flux, the gradients of the fields, the vertical current density, etc. In this paper, we extend the relevant feature set to include characteristics of the magnetic field that are based purely on the geometry and topology of 2D magnetogram images and show that this improves the prediction accuracy of a neural-net based flare-prediction method.

astro-ph.SR↗

arXiv2019

Birkhoff Averages and Rotational Invariant Circles for Area-Preserving Maps

Rotational invariant circles of area-preserving maps are an important and well-studied example of KAM tori. John Greene conjectured that the locally most robust rotational circles have rotation numbers that are noble, i.e., have continued fractions with a tail of ones, and that, of these circles, the most robust has golden mean rotation number. The accurate numerical confirmation of these conjectures relies on the map having a time reversal symmetry, and these methods cannot be applied to more general maps. In this paper, we develop a method based on a weighted Birkhoff average for identifying chaotic orbits, island chains, and rotational invariant circles that do not rely on these symmetries. We use Chirikov's standard map as our test case, and also demonstrate that our methods apply to three other, well-studied cases.

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arXiv2017

Diffusion and Drift in Volume-Preserving Maps

A nearly-integrable dynamical system has a natural formulation in terms of actions, $y$ (nearly constant), and angles, $x$ (nearly rigidly rotating with frequency $Ω(y)$). We study angle-action maps that are close to symplectic and have a positive-definite twist, the derivative of the frequency map, $DΩ(y)$. When the map is symplectic, Nekhoroshev's theorem implies that the actions are confined for exponentially long times: the drift is exponentially small and numerically appears to be diffusive. We show that when the symplectic condition is relaxed, but the map is still volume-preserving, the actions can have a strong drift along resonance channels. Averaging theory is used to compute the drift for the case of rank-$r$ resonances. A comparison with computations for a generalized Froeschlé map in four-dimensions, shows that this theory gives accurate results for the rank-one case.

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arXiv2017

Designing a Finite-Time Mixer: Optimizing Stirring for Two-Dimensional Maps

Mixing of a passive scalar in a fluid flow results from a two part process in which large gradients are first created by advection and then smoothed by diffusion. We investigate methods of designing efficient stirrers to optimize mixing of a passive scalar in a two-dimensional nonautonomous, incompressible flow over a finite time interval. The flow is modeled by a sequence of area-preserving maps whose parameters change in time, defining a mixing protocol. Stirring efficiency is measured by a negative Sobolev seminorm; its decrease implies creation of fine scale structure. A Perron-Frobenius operator is used to numerically advect the scalar for two examples: compositions of Chirikov standard maps and of Harper maps. In the former case, we find that a protocol corresponding to a single vertical shear composed with horizontal shearing at all other steps is nearly optimal. For the Harper maps, we devise a predictive, one-step scheme to choose appropriate fixed point stabilities and to control the Fourier spectrum evolution to obtain a near optimal protocol.

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arXiv2015

Mixed Dynamics in a Parabolic Standard Map

We use numerical and analytical tools to demonstrate arguments in favor of the existence of a family of smooth, symplectic diffeomorphisms of the two-dimensional torus that have both a positive measure set with positive Lyapunov exponent and a positive measure set with zero Lyapunov exponent. The family we study is the unfolding of an almost-hyperbolic diffeomorphism on the boundary of the set of Anosov diffeomorphisms, proposed by Lewowicz.

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arXiv2015

Thirty Years of Turnstiles and Transport

To characterize transport in a deterministic dynamical system is to compute exit time distributions from regions or transition time distributions between regions in phase space. This paper surveys the considerable progress on this problem over the past thirty years. Primary measures of transport for volume-preserving maps include the exiting and incoming fluxes to a region. For area-preserving maps, transport is impeded by curves formed from invariant manifolds that form partial barriers, e.g., stable and unstable manifolds bounding a resonance zone or cantori, the remnants of destroyed invariant tori. When the map is exact volume preserving, a Lagrangian differential form can be used to reduce the computation of fluxes to finding a difference between the action of certain key orbits, such as homoclinic orbits to a saddle or to a cantorus. Given a partition of phase space into regions bounded by partial barriers, a Markov tree model of transport explains key observations, such as the algebraic decay of exit and recurrence distributions.

nlin.CD↗

arXiv2012

Transport in Transitory, Three-Dimensional, Liouville Flows

We derive an action-flux formula to compute the volumes of lobes quantifying transport between past- and future-invariant Lagrangian coherent structures of n-dimensional, transitory, globally Liouville flows. A transitory system is one that is nonautonomous only on a compact time interval. This method requires relatively little Lagrangian information about the codimension-one surfaces bounding the lobes, relying only on the generalized actions of loops on the lobe boundaries. These are easily computed since the vector fields are autonomous before and after the time-dependent transition. Two examples in three-dimensions are studied: a transitory ABC flow and a model of a microdroplet moving through a microfluidic channel mixer. In both cases the action-flux computations of transport are compared to those obtained using Monte Carlo methods.

math.DS↗

arXiv2011

Symmetry Reduction by Lifting for Maps

We study diffeomorphisms that have one-parameter families of continuous symmetries. For general maps, in contrast to the symplectic case, existence of a symmetry no longer implies existence of an invariant. Conversely, a map with an invariant need not have a symmetry. We show that when a symmetry flow has a global Poincaré section there are coordinates in which the map takes a reduced, skew-product form, and hence allows for reduction of dimensionality. We show that the reduction of a volume-preserving map again is volume preserving. Finally we sharpen the Noether theorem for symplectic maps. A number of illustrative examples are discussed and the method is compared with traditional reduction techniques.

nlin.CD↗

arXiv2011

Resonances and Twist in Volume-Preserving Mappings

The phase space of an integrable, volume-preserving map with one action and $d$ angles is foliated by a one-parameter family of $d$-dimensional invariant tori. Perturbations of such a system may lead to chaotic dynamics and transport. We show that near a rank-one, resonant torus these mappings can be reduced to volume-preserving "standard maps." These have twist only when the image of the frequency map crosses the resonance curve transversely. We show that these maps can be approximated---using averaging theory---by the usual area-preserving twist or nontwist standard maps. The twist condition appropriate for the volume-preserving setting is shown to be distinct from the nondegeneracy condition used in (volume-preserving) KAM theory.

nlin.CD↗

arXiv2011

The Destruction of Tori in Volume-Preserving Maps

Invariant tori are prominent features of symplectic and volume preserving maps. From the point of view of chaotic transport the most relevant tori are those that are barriers, and thus have codimension one. For an $n$-dimensional volume-preserving map, such tori are prevalent when the map is nearly "integrable," in the sense of having one action and $n-1$ angle variables. As the map is perturbed, numerical studies show that the originally connected image of the frequency map acquires gaps due to resonances and domains of nonconvergence due to chaos. We present examples of a three-dimensional, generalized standard map for which there is a critical perturbation size, $ε_c$, above which there are no tori. Numerical investigations to find the "last invariant torus" reveal some similarities to the behavior found by Greene near a critical invariant circle for area preserving maps: the crossing time through the newly destroyed torus appears to have a power law singularity at $ε_c$, and the local phase space near the critical torus contains many high-order resonances.

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arXiv2010

Transport in Transitory Dynamical Systems

We introduce the concept of a "transitory" dynamical system---one whose time-dependence is confined to a compact interval---and show how to quantify transport between two-dimensional Lagrangian coherent structures for the Hamiltonian case. This requires knowing only the "action" of relevant heteroclinic orbits at the intersection of invariant manifolds of "forward" and "backward" hyperbolic orbits. These manifolds can be easily computed by leveraging the autonomous nature of the vector fields on either side of the time-dependent transition. As illustrative examples we consider a two-dimensional fluid flow in a rotating double-gyre configuration and a simple one-and-a-half degree of freedom model of a resonant particle accelerator. We compare our results to those obtained using finite-time Lyapunov exponents and to adiabatic theory, discussing the benefits and limitations of each method.

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