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We continue studies of the nonlocal erosion equation that is used as a mathematical model of the formation of a spatially inhomogeneous relief on semiconductor surfaces. We show that such a relief can form as a result of local bifurcations in the case where the stability of the spatially homogeneous equilibrium state changes. We consider a periodic boundary-value problem and study its codimension- bifurcations. For solutions describing an inhomogeneous relief, we obtain asymptotic formulas and study their stability. The analysis of the mathematical problem is based on modern methods of the theory of dynamical systems with an infinite-dimensional phase space, in particular, on the method of integral manifolds and on the theory of normal forms. [ABSTRACT FROM AUTHOR]

Several spectral radii formulas for infinite bounded non-negative matrices in max algebra are obtained. We also prove some Perron–Frobenius type results for such matrices. In particular, we obtain results on block triangular forms, which are similar to results on Frobenius normal form of $ n \times n $ n × n matrices. Some continuity results are also established. [ABSTRACT FROM AUTHOR]

In this paper, by extending the controllability and Brunovsky indices for a matrix pair to a matrix quadruple, three kinds of indices, say, the invertibility indices, the left invertibility indices, and the right invertibility indices, for linear time-invariant systems are introduced and studied. Based on properties of these indices, a neat expression for the Morse lists of a linear system is given without transforming it into its Morse normal form, which is a deep and fundamental result in linear systems theory, and takes an important role in many analysis and design problems for linear systems. Furthermore, the Morse normal form with only algebraic equivalence transformation is also investigated and is simplified. [ABSTRACT FROM AUTHOR]

The existence of simple uncoupled no-regret learning dynamics that converge to correlated equilibria in normal-form games is a celebrated result in the theory ofmulti-agent systems. Specifically, it has been known for more than 20 years that when all players seek to minimize their internal regret in a repeated normalform game, the empirical frequency of play converges to a normal-form correlated equilibrium. Extensiveform (that is, tree-form) games generalize normal-form games by modeling both sequential and simultaneous moves, as well as imperfect information. Because of the sequential nature and presence of private information in the game, correlation in extensive-form games possesses significantly different properties than in normalform games, many of which are still open research directions. Extensive-form correlated equilibrium (EFCE) has been proposed as the natural extensive-form counterpart to the classical notion of correlated equilibrium in normal-form games. Compared to the latter, the constraints that define the set of EFCEs are significantly more complex, as the correlation device (a.k.a. mediator) must take into account the evolution of beliefs of each player as they make observations throughout the game. Due to that significant added complexity, the existence of uncoupled learning dynamics leading to an EFCE has remained a challenging open research question for a long time. In this article, we settle that question by giving the first uncoupled no-regret dynamics that converge to the set of EFCEs in n-player general-sum extensive-form games with perfect recall.We show that each iterate can be computed in time polynomial in the size of the game tree, and that, when all players play repeatedly according to our learning dynamics, the empirical frequency of play after T game repetitions is proven to be a O(1/√ T )-approximate EFCE with high probability, and an EFCE almost surely in the limit. [ABSTRACT FROM AUTHOR]

The computation of the normal form as well as its unfolding is a key step to understand the topological structure of a bifurcation. Though a lot of results have been obtained, it still remains unsolved for higher co-dimensional bifurcations. The main purpose of this paper is devoted to the computation of a codimension-3 zero-Hopf–Hopf bifurcation, at which a zero as well as two pairs of pure imaginary eigenvalues can be found from the matrix evaluated at the equilibrium point. Different distributions of eigenvalues are considered, which may behave in a non-semisimple form for 1:1 internal resonance. Based on the combination of center manifold and normal form theory, all the coefficients of normal forms and nonlinear transformations are derived explicitly in terms of parameters of the original vector field, which are obtained via a recursive procedure. Accordingly, a user friendly computer program using a symbolic computation language Maple is developed to compute the coefficients up to an arbitrary order for a specific vector field with zero-Hopf–Hopf bifurcation. Furthermore, universal unfolding parameters are derived in terms of the perturbation of physical parameters, which can be employed to investigate the local behaviors in the neighborhood of the bifurcation point. Here, we emphasize that though different norm forms based on different choices may exist, their topological structures are the same, corresponding to qualitatively equivalent dynamics. [ABSTRACT FROM AUTHOR]

We give formal normal forms for parabolic logarithmic transseries f = z, with respect to parabolic logarithmic normalizations. Normalizations are given algorithmically, using fixed point theorems, as limits of Picard's sequences in appropriate complete metric spaces, in contrast to transfinite term-by-term eliminations described in former works. Furthermore, we give the explicit formula for the residual coefficient in the normal form and show that, in the larger logarithmic class, we can even eliminate the residual term from the normal form. [ABSTRACT FROM AUTHOR]

In our earlier research (see [Katsanikas & Wiggins, 2021a, 2021b, 2023a, 2023b, 2023c]), we developed two methods for creating dividing surfaces, either based on periodic orbits or two-dimensional generating surfaces. These methods were specifically designed for Hamiltonian systems with three or more degrees of freedom. Our prior work extended these dividing surfaces to more complex structures such as tori or cylinders, all within the energy surface of the Hamiltonian system. In this paper, we introduce a new method for constructing dividing surfaces. This method differs from our previous work in that it is based on 3D surfaces or geometrical objects, rather than periodic orbits or 2D generating surfaces (see [Katsanikas & Wiggins, 2023a]). To explain and showcase the new method and to present the structure of these 3D surfaces, the paper provides examples involving Hamiltonian systems with three degrees of freedom. These examples cover both uncoupled and coupled cases of a quadratic normal form Hamiltonian system. Our current paper is the first in a series of two papers on this subject. This research is likely to be of interest to scholars and researchers in the field of Hamiltonian systems and dynamical systems, as it introduces innovative approaches to constructing dividing surfaces and exploring their applications. [ABSTRACT FROM AUTHOR]

We study the local dynamics of the delay logistic equation with an additional feedback containing a large delay. Critical cases in the problem of stability of the zero equilibrium state are identified, and it is shown that they are infinite-dimensional. The well-known methods for studying local dynamics based on the theory of invariant integral manifolds and normal forms do not apply here. The methods of infinite-dimensional normalization proposed by the author are used and developed. As the main results, special nonlinear boundary value problems of parabolic type are constructed, which play the role of normal forms. They determine the leading terms of the asymptotic expansions of solutions of the original equation and are called quasinormal forms. [ABSTRACT FROM AUTHOR]

In our previous work, we developed two methods for generalizing the construction of a periodic orbit dividing surface for a Hamiltonian system with three or more degrees of freedom. Starting with a periodic orbit, we extend it to form a torus or cylinder, which then becomes a higher-dimensional object within the energy surface (see [Katsanikas & Wiggins, 2021a, 2021b, 2023a, 2023b]). In this paper, we present two methods to construct dividing surfaces not from periodic orbits but by using 2D surfaces (2D geometrical objects) in a Hamiltonian system with three degrees of freedom. To illustrate the algorithm for this construction, we provide benchmark examples of three-degree-of-freedom Hamiltonian systems. Specifically, we employ the uncoupled and coupled cases of the quadratic normal form of a Hamiltonian system with three degrees of freedom. [ABSTRACT FROM AUTHOR]

This paper investigates the complex dynamics of a ratio-dependent predator–prey model incorporating the Allee effect in prey and predator harvesting. To explore the joint effect of the harvesting effort and diffusion on the dynamics of the system, we perform the following analyses: (a) The stability of non-negative constant steady states; (b) The sufficient conditions for the occurrence of a Hopf bifurcation, Turing bifurcation, and Turing–Hopf bifurcation; (c) The derivation of the normal form near the Turing–Hopf singularity. Moreover, we provide numerical simulations to illustrate the theoretical results. The results demonstrate that the small change in harvesting effort and the ratio of the diffusion coefficients will destabilize the constant steady states and lead to the complex spatiotemporal behaviors, including homogeneous and inhomogeneous periodic solutions and nonconstant steady states. Moreover, the numerical simulations coincide with our theoretical results. [ABSTRACT FROM AUTHOR]

Purpose: To classify bursting oscillations according to different co-dimension of bifurcation is meaningful to the theory of slow-fast dynamics. The paper tried to show all possible bursting oscillations in the neighborhood of fold-Hopf bifurcation point in a vector field. Methods: The study focused on two typical cases associated with fold-Hopf bifurcation in which one of two universal unfolding parameters of the normal form was replaced by low-frequency excitation. By employing the modified slow–fast analysis method, together with the bifurcation analysis of the generalized autonomous system, we presented the dynamical evolution of the vector field. Results: Three forms of 2-D bursting attractors in the full system had been obtained, the mechanism of which was obtained by overlapping the transformed phase portrait and the bifurcation of the generalized autonomous system. Non-synchronization between the state variables was observed, while the effect of some stable equilibrium states on full dynamics disappeared because of the short window for the existence. Fold limit cycle bifurcation resulted in dramatic change of spiking amplitude, which varied according to two different stable cycles. Conclusions: By considering the influence of stable attractors in every region divided by the bifurcation sets on the slow–fast dynamics, we obtained all the types of bursting oscillations associated with the special bifurcation. The scheme can be employed to investigate the slow–fast dynamics with other high co-dimensional bifurcations. [ABSTRACT FROM AUTHOR]

The study of formal stability of equilibrium positions of a multiparametric Hamiltonian system in a generic case is traditionally carried out using its normal form under the condition of the absence of resonances of small orders. In this paper we propose a method of symbolic computation of the condition of existence of a resonance of arbitrary order for a system with three degrees of freedom. It is shown that this condition for each resonant vector can be represented as a rational algebraic curve. By methods of computer algebra the rational parametrization of this curve for the case of an arbitrary resonance is obtained. A model example of some two-parameter system of pendulum type is considered. [ABSTRACT FROM AUTHOR]

An infinite horizon optimal control problem with general endpoint constraints is reduced to a family of standard problems on finite time intervals containing the conditional cost of the phase vector as a terminal term. A new version of the Pontryagin maximum principle containing an explicit characterization of the adjoint variable is obtained for the problem with a general asymptotic endpoint constraint. In the case of the problem with a free final state, this approach leads to a normal form version of the maximum principle formulated completely in the terms of the conditional cost function. [ABSTRACT FROM AUTHOR]

We consider the existence of invariant curves of real analytic reversible mappings which are quasi-periodic in the angle variables. By the normal form theorem, we prove that under some assumptions, the original mapping is changed into its linear part via an analytic convergent transformation, so that invariants curves are obtained. In the iterative process, by solving the modified homological equations, we ensure that the transformed mapping is still reversible. As an application, we investigate the invariant curves of a class of nonlinear resonant oscillators, with the Birkhoff constants of the corresponding Poincaré mapping all zeros or not. [ABSTRACT FROM AUTHOR]

A perturbation bound for Williamson's symplectic normal form under any unitarily invariant norm has been derived in Idel et al. (2017) [3]. We improve this bound to a tight one, and derive a few alternative forms of our new bound. [ABSTRACT FROM AUTHOR]

We study the resurgence structure of a formal normalization of a certain vector field to the normal form using “mould calculus” developed by J. Écalle. We also describe the resurgence structure of transseries solutions of a nonlinear ordinary differential equation. [ABSTRACT FROM AUTHOR]

This paper considers a periodic boundary value problem for a nonlinear partial differential equation with a deviating spatial variable. It is called the nonlocal erosion equation and was proposed as a model for the formation of dynamic patterns on the semiconductor surface. As is demonstrated below, the formation of a spatially inhomogeneous relief is a self-organization process. An inhomogeneous relief appears due to local bifurcations in the neighborhood of homogeneous equilibria when they change their stability. The analysis of this problem is based on modern methods of the theory of infinite-dimensional dynamic systems, including such branches as the theory of invariant manifolds, the apparatus of normal forms, and asymptotic methods for studying dynamic systems. [ABSTRACT FROM AUTHOR]

The local dynamics of systems of two equations with delay is considered. The main assumption is that the delay parameter is large enough. Critical cases in the problem of the stability of the equilibrium state are identified, and it is shown that they are of infinite dimension. Methods of infinite-dimensional normalization are used and further developed. The main result is the construction of special nonlinear boundary value problems that play the role of normal forms. Their nonlocal dynamics determine the behavior of all solutions of the original system in a neighborhood of the equilibrium state. [ABSTRACT FROM AUTHOR]

Chains of Van der Pol equations with a large delay in coupling are considered. It is assumed that the number of chain elements is also sufficiently large. In a natural manner, a chain is replaced by a Van der Pol equation with an integral term in the space variable and with periodic boundary conditions. Primary attention is given to the local dynamics of chains with unidirectional and bidirectional coupling. For sufficiently large values of the delay parameter, parameters are explicitly determined for which critical cases occur in the stability problem for the zero equilibrium state. It is shown that the problems under consideration have an infinite-dimensional critical case. The well-known methods of invariant integral manifolds and the methods of normal forms are inapplicable in these problems. Proposed by this paper's author, the method of infinite normalization—the method of quasi-normal forms—is used to show that the leading terms of the asymptotics of the original system are determined by solutions of (nonlocal) quasi-normal forms, i.e., special nonlinear boundary value problems of the parabolic type. As the main results, corresponding quasi-normal forms are constructed for the considered chains. [ABSTRACT FROM AUTHOR]

The universal unfolding of a normal form can be employed to reveal the general behaviors of a specific local bifurcation, while the computation of the normal form for high codimensional bifurcation still remains unsolved. This paper focuses on a vector field with codimension-3 triple Hopf bifurcation. Besides 1:1 internal resonance for two frequencies in semi-simple form, two cases are considered, corresponding to internal resonance and noninternal resonance between the first two frequencies and the third frequency, respectively. Based on a combination of center manifold and normal theory, all the coefficients in the normal form and the nonlinear transformation are derived explicitly in terms of the coefficients of the original vector field. Upon the recursive procedure established, a user friendly computer program can be easily developed using a symbolic computation language Maple to compute the coefficients up to an arbitrary order for a specific vector field with triple Hopf bifurcation. Furthermore, universal unfolding of the normal form is obtained, which can be used to display the topological structure in the neighborhood of bifurcation point. It is pointed out that different choices of the remaining terms in the nonlinear transformation may lead to different expressions of the normal form and the unfolding, which are qualitatively equivalent to each other. [ABSTRACT FROM AUTHOR]

We study bifurcation behavior in periodic perturbations of two-dimensional symmetric systems exhibiting codimension-two bifurcations with a double zero eigenvalue when the frequencies of the perturbation terms are small. We transform the periodically perturbed systems to simpler ones which are periodic perturbations of the normal forms for the codimension-two bifurcations, and apply the subharmonic and homoclinic Melnikov methods to analyze bifurcations occurring there. In particular, we show that there exist transverse homoclinic or heteroclinic orbits, which yield chaotic dynamics, in wide parameter regions. These results can be applied to three or higher-dimensional systems and even to infinite-dimensional systems with the assistance of center manifold reduction and the invariant manifold theory. We illustrate our theory for a pendulum subjected to position and velocity feedback control when the desired position is periodic in time. We also give numerical computations by the computer tool AUTO to demonstrate the theoretical results. [ABSTRACT FROM AUTHOR]

We investigate the solution sets to equations in the solvable Baumslag-Solitar groups B S (1 , k) , k ≥ 2 , and show that these sets are represented by edt0l languages in some cases. In particular, we prove that the multiplication table of such a group forms an edt0l language with respect to a specific natural normal form for group elements. [ABSTRACT FROM AUTHOR]

In this paper, we consider a constructive proof of the termination of the normal form (NF) algorithm for multivariate polynomials, as well as the related concept of admissible ordering < on monomials. In classical mathematics, the well-quasiorder property of relation < is derived from Dickson's lemma, and this is sufficient to justify the termination of the NF algorithm. In provable programming based on constructive type theory (Coq and Agda), a somewhat stronger condition (in constructive mathematics) of the well-foundedness of the ordering (in its constructive version) is required. We propose a constructive proof of this theorem (T) for < , which is based on a known method that we refer to here as the "pattern method." This theorem on the well-foundedness of an arbitrary admissible ordering is also important in itself, independently of the NF algorithm. We are not aware of any other works on constructive proof of this theorem. However, it turns out that it follows, not very difficultly, from the results achieved by other researchers in 2003. We program this proof in the Agda language in the form of our library AdmissiblePPO-wellFounded of provable computational algebra programs. This development also uses the theorem to prove termination of the NF algorithm for polynomials. Thus, the library also contains a set of provable programs for polynomial algebra, which is significantly larger than that needed to prove Theorem T. [ABSTRACT FROM AUTHOR]

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In this paper, we revisit the greatest common right divisor (GCRD) extraction from a set of polynomial matrices ... with coefficients in a generic field F and with common column dimension n. We give necessary and sufficient conditions for a matrix G(λ)∈F[λ]]lxn to be a GCRD using the Smith normal form of the m x n compound matrix P(λ) obtained by concatenating Pi(λ) vertically, where ... We also describe the complete set of degrees of freedom for the solution G(λ), and we link it to the Smith form and Hermite form of P(λ). We then give an algorithm for constructing a particular minimum size solution for this problem when F=C or R, using state-space techniques. This new method works directly on the coefficient matrices of P(λ)., using orthogonal transformations only. The method is based on the staircase algorithm, applied to a particular pencil derived from a generalized state-space model of P(λ). [ABSTRACT FROM AUTHOR]

Let A be a d × d matrix with rational entries which has no eigenvalue λ ∈ C of absolute value | λ | < 1 and let Z d [ A ] be the smallest nontrivial A-invariant Z -module. We lay down a theoretical framework for the construction of digit systems (A , D) , where D ⊂ Z d [ A ] finite, that admit finite expansions of the form x = d 0 + A d 1 + ⋯ + A ℓ − 1 d ℓ − 1 (ℓ ∈ N , d 0 , ... , d ℓ − 1 ∈ D) for every element x ∈ Z d [ A ]. We put special emphasis on the explicit computation of small digit sets D that admit this property for a given matrix A, using techniques from matrix theory, convex geometry, and the Smith Normal Form. Moreover, we provide a new proof of general results on this finiteness property and recover analogous finiteness results for digit systems in number fields a unified way. [ABSTRACT FROM AUTHOR]

Recently, we presented two methods of constructing periodic orbit dividing surfaces for Hamiltonian systems with three or more degrees of freedom [Katsanikas & Wiggins, 2021a, 2021b]. These methods were illustrated with an application to a quadratic normal form Hamiltonian system with three degrees of freedom. More precisely, in these papers we constructed a section of the dividing surfaces that intersect with the hypersurface x = 0. This was motivated by studies in reaction dynamics since in this model reaction occurs when the sign of the x coordinate changes. In this paper, we continue the work of the third paper [Katsanikas & Wiggins, 2023] of this series of papers to construct the full dividing surfaces that are obtained by our algorithms and to prove the no-recrossing property. In the third paper we did this for the dividing surfaces of the first method [Katsanikas & Wiggins, 2021a]. Now we are doing the same for the dividing surfaces of the second method [Katsanikas & Wiggins, 2021b]. In addition, we computed the dividing surfaces of the second method for a coupled case of the quadratic normal form Hamiltonian system and we compared our results with those of the uncoupled case. This paper completes this series of papers about the construction of periodic orbit dividing surfaces for Hamiltonian systems with three or more degrees of freedom. [ABSTRACT FROM AUTHOR]

As a kind of dynamical system with a particular nonlinear structure, a multi-time scale nonlinear system is one of the essential directions of the current development of nonlinear dynamics theory. Multi-time scale nonlinear systems in practical applications are often complex forms of coupling of high-dimensional and high codimension characteristics, leading to various complex bursting oscillation behaviors and bifurcation characteristics in the system. For exploring the complex bursting dynamics caused by high codimension bifurcation, this paper considers the normal form of the vector field with triple zero bifurcation. Two kinds of codimension-2 bifurcation that may lead to complex bursting oscillations are discussed in the two-parameter plane. Based on the fast–slow analysis method, by introducing the slow variable W = A sin (ω t) , the evolution process of the motion trajectory of the system changing with W was investigated, and the dynamical mechanism of several types of bursting oscillations was revealed. Finally, by varying the frequency of the slow variable, a class of chaotic bursting phenomena caused by the period-doubling cascade is deduced. Developing related work has played a positive role in deeply understanding the nature of various complex bursting phenomena and strengthening the application of basic disciplines such as mechanics and mathematics in engineering practice. [ABSTRACT FROM AUTHOR]

In this paper, we prove an abstract KAM (Kolmogorov–Arnold–Moser) theorem for infinite dimensional reversible Schrödinger systems. Using this KAM theorem together with partial Birkhoff normal form method, we obtain the existence of quasi-periodic solutions for a class of completely resonant reversible coupled nonlinear Schrödinger systems on two dimensional torus. [ABSTRACT FROM AUTHOR]

The main focus of the present research work is to analyze the non-linear stability of the triangular equilibrium points and in the restricted three-body problem (R3BP). The condition of stability has been found out under the influence of the heterogeneous primary and a radiating finite-straight segment secondary and also under the effect by Coriolis as well as Centrifugal forces. This piece of research has been done by doing the normalization of the Hamiltonian in order to attained the Birkhoff's normal form of the Hamiltonian, since normal forms of Hamiltonian are important to study the non-linear stability of equilibrium points. The conditions of KAM Theorem have been examined in the presence of resonance cases and and found that these conditions have been failed for three values of mass ratios and Except these three values, and are stable in non-linear sense within the range of linear stability where is the critical value of mass parameter Consequently, in the presence of above mentioned purturbations the triangular equilibrium points are unstable for these three values of mass ratios. [ABSTRACT FROM AUTHOR]

In this article we study the semiclassical resolvent estimate for the non-selfadjoint Baouendi–Grushin operator on the two-dimensional torus T 2 = R 2 / (2 π Z) 2 with Hölder dampings. The operator is subelliptic degenerating along the vertical direction at x = 0 . We exhibit three different situations: (i) the damping region verifies the geometric control condition with respect to both the non-degenerate Hamiltonian flow and the vertical subelliptic flow; (ii) the undamped region contains a horizontal strip; (iii) the undamped part is a horizontal line. In all of these situations, we obtain sharp resolvent estimates. Consequently, we prove the optimal energy decay rate for the associated damped waved equations. For (i) and (iii), our results are in sharp contrast to the Laplace resolvent since the optimal bound is governed by the quasimodes in the subelliptic regime. While for (ii), the optimality is governed by the quasimodes in the elliptic regime, and the optimal energy decay rate is the same as for the classical damped wave equation on T 2 . Our analysis contains the study of adapted two-microlocal semiclassical measures, construction of quasimodes and refined Birkhoff normal-form reductions in different regions of the phase-space. Of independent interest, we also obtain the propagation theorem for semiclassical measures of quasimodes microlocalized in the subelliptic regime. [ABSTRACT FROM AUTHOR]

In this paper we introduce the notion of fractal codimension of a nilpotent contact point p , for λ = λ 0 , in smooth planar slow–fast systems X ϵ , λ when the contact order n λ 0 (p) of p is even, the singularity order s λ 0 (p) of p is odd and p has finite slow divergence, i.e., s λ 0 (p) ≤ 2 (n λ 0 (p) − 1). The fractal codimension of p is a generalization of the "traditional" codimension of a slow-fast Hopf point of Liénard type, introduced in (Dumortier and Roussarie (2009) [7]), and it is intrinsically defined, i.e., it can be directly computed without the need to first bring the system into its normal form. The intrinsic nature of the notion of fractal codimension stems from the Minkowski dimension of fractal sequences of points, defined near p using the so-called entry-exit relation, and slow divergence integral. We apply our method to a slow-fast Hopf point and read its degeneracy (i.e., the first nonzero Lyapunov quantity) as well as the number of limit cycles near such a Hopf point directly from its fractal codimension. We demonstrate our results numerically on some interesting examples by using a simple formula for computation of the fractal codimension. [ABSTRACT FROM AUTHOR]

Chains of coupled van der Pol equations are considered. The main assumption that motivates the use of special asymptotic methods is that the number of elements in the chain is sufficiently large. This allows moving from a discrete system of equations to the use of a continuity argument and obtaining an integro-differential boundary value problem as the initial model. In the study of the behaviour of all its solutions in a neighbourhood of the equilibrium state, infinite-dimensional critical cases arise in the problem of the stability of solutions. The main results include the construction of special families of quasi-normal forms, namely non-linear boundary value problems of either Schrödinger or Ginzburg–Landau type. Their solutions make it possible to determine the main terms of the asymptotic expansion of both regular and irregular solutions to the original system. The main goal is the study of chains with diffusion- and advective-type couplings, as well as fully connected chains. [ABSTRACT FROM AUTHOR]

Graph products of monoids provide a common framework for direct and free products, and graph monoids (also known as free partially commutative monoids). If the monoids in question are groups then any graph product is a group. For monoids that are not groups, regularity is perhaps the first and most important algebraic property that one considers: however, graph products of regular monoids are not in general regular. We show that a graph product of regular monoids satisfies the related, but weaker, condition of being abundant. More generally, we show that the classes of left abundant and left Fountain monoids are closed under graph product. As a very special case we obtain the earlier result of Fountain and Kambites that the graph product of right cancellative monoids is right cancellative. To achieve our aims we show that elements in (arbitrary) graph products have a unique Foata normal form, and give some useful reduction results; these may equally well be applied to groups as to the broader case of monoids. [ABSTRACT FROM AUTHOR]

We prove a normal form for contact forms close to a Zoll one and deduce that Zoll contact forms on any closed manifold are local maximizers of the systolic ratio. Corollaries of this result are: (1) sharp local systolic inequalities for Riemannian and Finsler metrics close to Zoll ones, (2) the perturbative case of a conjecture of Viterbo on the symplectic capacity of convex bodies, (3) a generalization of Gromov's non-squeezing theorem in the intermediate dimensions for symplectomorphisms that are close to linear ones. [ABSTRACT FROM AUTHOR]

In this paper, we consider a general reaction-diffusion system with nonlocal effects and Neumann boundary conditions, where a spatial average kernel is chosen to be the nonlocal kernel. By virtue of the center manifold reduction technique and normal form theory, we present a new algorithm for computing normal forms associated with the codimension-two double Hopf bifurcation. The theoretical results are applied to a predator-prey model, and complex dynamic behaviors such as spatially nonhomogeneous periodic oscillations and spatially nonhomogeneous quasi-periodic oscillations could occur. [ABSTRACT FROM AUTHOR]

We revisit the damped wave equation on two-dimensional torus where the damped region does not satisfy the geometric control condition. It was shown in [ 1 ] that, for sufficiently regular damping, the damped wave equation is stale at a rate sufficiently close to |$t^{-1}$|⁠. We show that if the damping vanishes like a Hölder function |$|x|^{\beta }$|⁠ , and in addition, the boundary of the damped region is locally strictly convex with positive curvature, the wave is stable at rate |$t^{-1+\frac {2}{2\beta +7}}$|⁠ , which is better than the known optimal decay rate |$t^{-1+\frac {1}{\beta +3}}$| for strip-shaped dampings of the same Hölder regularity. Moreover, we show by example that the decay rate is optimal. This illustrates the fact that the sharp energy decay rate depends not only on the order of vanishing of the damping but also on the shape of the damped region. The main ingredient of the proof is the averaging method (normal form reduction) developed by Hitrik and Sjöstrand ([ 20 ], [ 35 ]). [ABSTRACT FROM AUTHOR]

The well-known Van der Pol equation with delayed feedback is considered. It is assumed that the delay factor is large enough. In the study of the dynamics, the critical cases in the problem of the stability of the zero equilibrium state are identified. It is shown that they have infinite dimension. For such critical cases, special local analysis methods have been developed. The main result is the construction of nonlinear evolutionary boundary value problems, which play the role of normal forms. Such boundary value problems can be equations of the Ginzburg–Landau type, as well as equations with delay and special nonlinearity. The nonlocal dynamics of the constructed equations determines the local behavior of the solutions to the original equation. It is shown that similar normalized boundary value problems also arise for the Van der Pol equation with a large coefficient of the delay equation. The important problem of a small perturbation containing a large delay is considered separately. In addition, the Van der Pol equation, in which the cubic nonlinearity contains a large delay, is considered. One of the general conclusions is that the dynamics of the Van der Pol equation in the presence of a large delay is complex and diverse. It fundamentally differs from the dynamics of the classical Van der Pol equation. [ABSTRACT FROM AUTHOR]

We find the normal forms of hyperbolic logarithmic transseries with respect to parabolic logarithmic normalizing changes of variables. We provide a necessary and sufficient condition on such transseries for the normal form to be linear. The normalizing transformations are obtained via fixed point theorems, and are given algorithmically, as limits of Picard sequences in appropriate topologies. [ABSTRACT FROM AUTHOR]

The first extended greatest common right divisor (GCRD) algorithm for parametric univariate polynomial matrices is presented. The starting point of this GCRD algorithm is the free property of submodules over univariate polynomial rings. We convert the computation of GCRDs to that of free basis for modules and prove that a free basis of the submodule generated by row vectors of input matrices forms just a GCRD of these matrices. The GCRD algorithm is obtained by computing a minimal Gröbner basis for the corresponding submodule since a minimal Gröbner basis of submodules is a free basis for univariate cases. While the key idea of extended algorithm is to construct a special module by adding the unit vectors which can record the representation coefficients. This method based on modules can be naturally generalized to the parametric case because of the comprehensive Gröbner systems for modules. As a consequence, we obtain an extended GCRD algorithm for parametric univariate polynomial matrices. More importantly, we apply the proposed extended GCD algorithm for univariate polynomials (as a special case of matrices) to the computation of Smith normal form, and give the first algorithm for reducing a univariate polynomial matrix with parameters to its Smith normal form. [ABSTRACT FROM AUTHOR]

For decades, the network-organized reaction-diffusion models have been widely used to study ecological and epidemiological phenomena in discrete space. However, the high dimensionality of these nonlinear systems places a long-standing restriction to develop the normal forms of various bifurcations. In this paper, we take an important step to present a rigorous procedure for calculating the normal form associated with the Hopf bifurcation of the general network-organized reaction-diffusion systems, which is similar to but can be much more intricate than the corresponding procedure for the extensively explored PDE systems. To show the potential applications of our obtained theoretical results, we conduct the detailed Hopf bifurcation analysis for a multi-patch predator-prey system defined on any undirected connected underlying network and on the particular non-periodic one-dimensional lattice network. Remarkably, we reveal that the structure of the underlying network imposes a significant effect on the occurrence of the spatially nonhomogeneous Hopf bifurcations. [ABSTRACT FROM AUTHOR]

A central challenge in physics is to describe non-equilibrium systems driven by randomness, such as a randomly growing interface, or fluids subject to random fluctuations that account e.g. for local stresses and heat fluxes in the fluid which are not related to the velocity and temperature gradients. For deterministic systems with infinitely many degrees of freedom, normal form and center manifold theory have shown a prodigious efficiency to often completely characterize how the onset of linear instability translates into the emergence of nonlinear patterns, associated with genuine physical regimes. However, in presence of random fluctuations, the underlying reduction principle to the center manifold is seriously challenged due to large excursions caused by the noise, and the approach needs to be revisited. In this study, we present an alternative framework to cope with these difficulties exploiting the approximation theory of stochastic invariant manifolds, on one hand, and energy estimates measuring the defect of parameterization of the high-modes, on the other. To operate for fluid problems subject to stochastic stirring forces, these error estimates are derived under assumptions regarding dissipation effects brought by the high-modes in order to suitably counterbalance the loss of regularity due to the nonlinear terms. As a result, the approach enables us to predict, from reduced equations of the stochastic fluid problem, the occurrence in large probability of a stochastic analogue to the pitchfork bifurcation, as long as the noise's intensity and the eigenvalue's magnitude of the mildly unstable mode scale accordingly. In the case of SPDEs forced by a multiplicative noise in the orthogonal subspace of e.g. its mildly unstable mode, our parameterization formulas show that the noise gets transmitted to this mode via non-Markovian coefficients, and that the reduced equation is only stochastically driven by the latter. These coefficients depend explicitly on the noise path's history, and their memory content is self-consistently determined by the intensity of the random force and its interaction through the SPDE's nonlinear terms. Applications to a stochastic Rayleigh-Bénard problem are detailed, for which conditions for a stochastic pitchfork bifurcation (in large probability) to occur, are clarified. [ABSTRACT FROM AUTHOR]

In this paper, two-dimensional completely resonant Schrödinger equation with the general nonlinearity i u t − Δ u + | u | 2 p u = 0 , x ∈ T 2 : = R 2 / (2 π Z) 2 , t ∈ R , p ∈ Z + under periodic boundary conditions is considered. For any given positive integers p and b , it is obtained that a Whitney smooth family of small-amplitude b -quasi-periodic solutions for the equation by developing an abstract KAM (Kolmogorov-Arnold-Moser) theorem for infinite dimensional Hamiltonian systems. The overall strategy in the proof of the KAM theorem is a normal form techniques sparsing angle-dependent terms, which can be achieved by choosing the appropriate tangential sites. The essence of the normal form is the integrable part of the Hamiltonian system after introducing the action-angle variable, which contains both the linear integrable part of the Schrödinger equation and the integrable part from the nonlinearity. Determining such normal form, in general, is not easy task as it requires some novel ideas and large number of complex calculations. This work includes some new ideas and overcomes some technical difficulties, which solves more completely the existence problem of quasi-periodic solutions of the completely resonant Schrödinger equation on the two dimensional torus with the general nonlinearity. [ABSTRACT FROM AUTHOR]

In this paper we show the existence of an infinite measure set of exponentially escaping orbits for a resonant Fermi accelerator, which is realised as a square billiard with a periodically oscillating platform. We use normal forms to describe the energy change in a period and employ techniques from the theory of hyperbolic systems with singularities to show the exponential drift given by these normal forms on a divided time-energy phase. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the spatiotemporal dynamics of the Sel'kov–Schnakenberg system. The stability of the positive constant steady state is studied by the linear stability theory. Hopf bifurcation and Turing–Hopf bifurcation are generated by varying two parameters in the model. The normal form near the Turing–Hopf singularity is calculated to explore the complex dynamics of the system. Finally, numerical simulations are carried out to verify the theoretical results. Our results show that the Sel'kov–Schnakenberg system exhibits complex dynamics near the Turing–Hopf singularity, including the existence of inhomogeneous steady states, homogeneous periodic solutions and inhomogeneous periodic solutions. [ABSTRACT FROM AUTHOR]

A real polynomial in two variables is considered. Its expansion near the zero critical point begins with a third-degree form. The simplest forms to which this polynomial is reduced with the help of invertible real local analytic changes of coordinates are found. First, for the cubic form, normal forms are obtained using linear changes of coordinates. Altogether, there are three of them. Then three nonlinear normal forms are obtained for the complete polynomial. Simplification of the calculation of a normal form is proposed. A meaningful example is given. [ABSTRACT FROM AUTHOR]

This is the first instance in the extensive literature of more than three decades for complete normal form classification of a singular family on a 2n-dimensional center manifold for arbitrary n. We are concerned with complete normal form characterization and classification of non-resonant n-tuple Hopf singular differential systems with radial and rotational nonlinearities. Our analysis is facilitated by using several reduction techniques. These include an invariant cell-decomposition of the state space, a family of smooth flow-invariant foliations, leaf-reduction of differential systems and leaf-normal forms. Each leaf of the foliations is a minimal flow-invariant realization of the state space for all radial and rotational differential systems. Complete simplest normal form characterization for singular flows are provided using a family of leaf-reductions and infinite level (simplest) formal leaf-normal forms. In this direction, we introduce Lie algebra structures on invariant leaf manifolds for the local leaf-normal classifications. Since leaf-manifolds foliate the state space, leaf normal forms for all flow-invariant leaves are required for a complete normal form characterization of the 2n-dimensional system. Thus, we further discuss the geometry and spectral impact of leaf variations on the infinite level leaf-normal form coefficients, leaf-finite determinacy and leaf-universal unfoldings. There are infinitely many leaf-systems for such a 2n-dimensional system. However, we show that a 2n-dimensional system can admit at most a finite number of topologically non-equivalent leaf-normal form systems. These are the ones that classify the 2n-dimensional singular family. [ABSTRACT FROM AUTHOR]