Computing a closest bifurcation instability in multidimensional parameter space

Summary Engineering and physical systems are often modeled as nonlinear differential equations with a vector λ of parameters and operated at a stable equilibrium. However, as the parameters λ vary from some nominal value λ₀, the stability of the equilibrium can be lost in a saddle-node or Hopf bifurcation. The spatial relation in parameter space of λ₀ to the critical set of parameters at which the stable equilibrium bifurcates determines the robustness of the system stability to parameter variations and is important in applications. We propose computing a parameter vector λ_* at which the stable equilibrium bifurcates which is locally closest in parameter space to the nominal parameters λ₀. Iterative and direct methods for computing these locally closest bifurcations are described. The methods are extensions of standard, one-parameter methods of computing bifurcations and are based on formulas for the normal vector to hypersurfaces of the bifurcation set. Conditions on the hypersurface curvature are given to ensure the local convergence of the iterative method and the regularity of solutions of the direct method. Formulas are derived for the curvature of the saddle node bifurcation set. The methods are extended to transcritical and pitchfork bifurcations and parametrized maps, and the sensitivity to λ₀ of the distance to a closest bifurcation is derived. The application of the methods is illustrated by computing the proximity to the closest voltage collapse instability of a simple electric power system.     

二重高阶对称破缺分歧点和它们的数值确定

本文考虑带Z_××Z₂对称性的两参数非线性的二重高阶对称破缺分歧点。利用对称性,我们提出了相应的正则扩张系统来确定这类分歧点。同时指出存在两条平方音叉式分歧点的道路通过该点。     

Bifurcation analysis in a simplified tri-neuron BAM network model with multiple delays

In this paper, we consider a three-dimensional delayed differential equation representing a bidirectional associate memory (BAM) neural network with three neurons and two discrete delays. By analyzing the number and stability of equilibria, the pitchfork bifurcation curve of the system is obtained. Furthermore, on the pitchfork bifurcation curve, by using the sum of two delays as the bifurcation parameter, we find that the system can undergo a Hopf bifurcation at the origin and the three-dimensional ordinary differential equation describing the flow on the center manifold is given.     

Effect of bifurcation on the semi-active optimal control problem

For nonlinear dynamic systems near bifurcation, the basins of attraction of fixed points as well as the steady-state responses can change considerably with a small variation of the bifurcating parameter. This paper studies the effect of bifurcation on the semi-active optimal control problem with fixed final state by using the cell mapping method. A system parameter is taken as the control. The admissible control values considered encompass a bifurcation point of the system. Global changes in the optimal control solution for different targets are studied. Saddle node, supercritical pitchfork and subcritical Hopf bifurcations are considered in the examples. It has been found that the global topology of the optimal control solution is strongly dependent on the state of the target.     

Dynamics of two-cell systems with discrete delays

We consider the system of delay differential equations (DDE) representing the models containing two cells with time-delayed connections. We investigate global, local stability and the bifurcations of the trivial solution under some generic conditions on the Taylor coefficients of the DDE. Regarding eigenvalues of the connection matrix as bifurcation parameters, we obtain codimension one bifurcations (including pitchfork, transcritical and Hopf bifurcation) and Takens-Bogdanov bifurcation as a codimension two bifurcation. For application purposes, this is important since one can now identify the possible asymptotic dynamics of the DDE near the bifurcation points by computing quantities which depend explicitly on the Taylor coefficients of the original DDE. Finally, we show that the analytical results agree with numerical simulations.     

COMPUTATION OF HOPF BRANCHES BIFURCATING FROM A HOPF/PITCHFORK POINT FOR PROBLEMS WITH Z_2-SYMMETRY

1.IntroductionThispaperisdevotedtothecalculatiollofT,ranchesofHopfpointswhichemallatefromacertaillsingularPointofatwopar:lmeterII()nlinearsystemwhereXisarealHillersspac(},Aabifllrcationparallleter,oranadditionalcontrolparameter,alldgisasnlootllmapping.\Nreassllllle(HI)gisA--synlnletric:thereexistsalillearoperators:X-Xsatisfying(I:identicaloperatorillX)Itiswellknottrnthat(1.2)irldllcestilesplittillgl)Th.firstauthorhasbeedsupportedbyar(>searchgralltoftileV'Olkswagen-StiftungWesaythatxiss…     

Double $S$-Breaking Cubic Turning Points and Their Computation

1.Introducti0nManynaturalphen0menapossessm0reorlessexactsymmetries,whicharelikelytobereflectedinanysensiblemathematicalm0del.Idealizationssuchasperiodicboundaryconditi0nscanproduceadditionaJsymmetries.Phen0menawhosemodelsexhibitbothsymmetryandnonlinearityleadtopr0blemswhicharechallengingandrichinc0mplexity.Problemswithsymmetriescanshowarichbifurcationbehavi0ur.Theoccurrenceofmultiplesteadystatebifurcationismostlyduetounderlyingsymmetries.Thisgivesrisetothedifficultiestonumericalcomputation-H…     

Homoclinic bifurcation with nonhyperbolic equilibria

The problem of homoclinic bifurcation is studied for a high dimensional system with nonhyperbolic equilibria. By constructing local coordinate systems near the unperturbed homoclinic orbit, Poincaré maps for the new system are established. Then the persistence of the homoclinic orbit and the bifurcation of the periodic orbit for the system accompanied with pitchfork bifurcation are obtained. Some known results are extended.     

Krylov methods and determinants for detecting bifurcations in one parameter dependent partial differential equations

In this paper, we study the computation of the sign of the determinant of a large matrix as a byproduct of the preconditioned GMRES method when applied to solve the linear systems arising in the discretization of partial differential equations (PDEs). Numerical experiments are presented where the technique is applied to detect and locate pitchfork and transcritical bifurcation points on a one parameter dependent system. With an appropriate selection of the initial guess in the GMRES method, the technique is shown to detect and accurately locate bifurcation points. We present an analysis that helps to explain the good performance observed in practice. AMS subject classification (2000) 65F40, 15A60, 65P30, 35B60, 65N35, 65F10     

一个分歧定理

本文用 Morse 理论给出 Krasnoselski Rabinowitz 关于位算子分歧点定理的一个新的证明.设 H 是一个 Hilbert 空间,Ω 是 H 中零元θ的一个邻域.又设 L 是 H 上的一个有界自伴算子,而 G∈C(Ω,H)满足 G(u)=o(‖u‖),当 u→θ.倘若 G 还是一个位算子,即存在 g∈C~1(Ω,R~1),使得 dg=G.求解带参数 λ∈R~1的方程     

The computation of symmetry-breaking bifurcation points inZ 2×Z 2-symmetric nonlinear problems

This paper is mainly concerned with corank-2 and corank-3 symmetry-breaking bifurcation point inZ ₂×Z ₂-symmetric nonlinear problems. Regular extended systems are used to compute corank-2 and corank-3 symmetry-breaking bifuracation points. Two numerical examples are given. In addition, we show that there exist three quadratic pitchfork bifurcation point curves passing through corank-2 symmetry-breaking bifurcation point. This project was supported by the National Natural Science Foundation of China and the State Key Project for Basic Resserch.     

计算立方体上Henon方程多个正解的分歧方法

本文首先应用分歧方法给出计算立方体上Henon方程边值问题D₄(3)对称正解的三种算法, 然后以Henon方程中的参数r为分歧参数, 在D₄(3)对称正解解枝上 用扩张系统方法求出对称破缺分歧点, 进而用解枝转接方法计算出其它具有不同对称性质的正解.     

Bifurcation analysis on a generalized recurrent neural network with two interconnected three-neuron components

A class of recurrent neural networks is constructed by generalizing a specific class of n-neuron networks. It is shown that the newly constructed network experiences generic pitchfork and Hopf codimension one bifurcations. It is also proved that the emergence of generic Bogdanov–Takens, pitchfork–Hopf and Hopf–Hopf codimension two, and the degenerate Bogdanov–Takens bifurcation points in the parameter space is possible due to the intersections of codimension one bifurcation curves. The occurrence of bifurcations of higher codimensions significantly increases the capability of the newly constructed recurrent neural network to learn broader families of periodic signals.     

Nonlinear analysis of a novel three-scroll chaotic system

This paper reports the nonlinear dynamics of a novel three-scroll chaotic system. The local stability of hyperbolic equilibrium and non-hyperbolic equilibrium are investigated by using center manifold theorem. Pitchfork bifurcation, degenerate pitchfork bifurcation and Hopf bifurcation are analyzed when the parameters are varied in the space of parameter. For a suitable choice of the parameters, the existence of singularly degenerate heteroclinic cycles and Hopf bifurcation without parameters are also investigated. Some numerical simulations are given to support the analytic results.     

一类双面碰撞振子的对称性尖点分岔与混沌

讨论了一类单自由度双面碰撞振子的对称型周期n-2运动以及非对称型周期n-2运动．把映射不动点的分岔理论运用到该模型,并通过分析对称系统的Poincaré映射的对称性,证明了对称型周期运动只能发生音叉分岔．数值模拟表明:对称系统的对称型周期n-2运动,首先由一条对称周期轨道通过音叉分岔形成具有相同稳定性的两条反对称的周期轨道;随着参数的持续变化,两条反对称的周期轨道经历两个同步的周期倍化序列各自生成一个反对称的混沌吸引子．如果对称系统演变为非对称系统,非对称型周期n-2运动的分岔过程可用一个两参数开折的尖点分岔描述,音叉分岔将会演变为一支没有分岔的分支以及另外一个鞍结分岔的分支．     

Dynamics of a Discrete Two-species Competitive Model with Michaelies-Menten Type Harvesting in the First Species

In this paper, we use a semidiscretization method to derive a discrete two-species competitive model with Michaelis-Menten type harvesting in the first species. First, the existence and local stability of fixed points of the system are investigated by employing a key lemma. Subsequently, the transcritical bifurcation, period-doubling bifurcation and pitchfork bifurcation of the model are investigated by using the Center Manifold Theorem and bifurcation theory. Finally, numerical simulations are presented to illustrate corresponding theoretical results.     

A Bayesian estimation of unfolded pitchfork bifurcation structure based upon experimental data

We consider the practical problem of estimating parameter valuesfor the unfolding of a pitchfork bifurcation from observed data.Although the existence of a bifurcation point may have beentheoretically determined, observed data from experiments ormeasurement must reflect the natural unfolding due to existingperturbations and imperfections. We demonstrate how a Bayesianapproach provides a natural formulation to this problem andhow incremental observations alter our best assessment of thetrue, unfolded, bifurcation structure, close to the prior estimate(the pitchfork). This method may be useful in practice to estimatethe location of bifurcation branches other than a particularone experimentally observed.     

Nonlinear rotating convection in a sparsely packed porous medium

We investigate linear and weakly nonlinear properties of rotating convection in a sparsely packed Porous medium. We obtain the values of Takens–Bogdanov bifurcation points and co-dimension two bifurcation points by plotting graphs of neutral curves corresponding to stationary and oscillatory convection for different values of physical parameters relevant to rotating convection in a sparsely packed porous medium near a supercritical pitchfork bifurcation. We derive a nonlinear two-dimensional Landau–Ginzburg equation with real coefficients by using Newell–Whitehead method [16]. We investigate the effect of parameter values on the stability mode and show the occurrence of secondary instabilities viz., Eckhaus and Zigzag Instabilities. We study Nusselt number contribution at the onset of stationary convection. We derive two nonlinear one-dimensional coupled Landau–Ginzburg type equations with complex coefficients near the onset of oscillatory convection at a supercritical Hopf bifurcation and discuss the stability regions of standing and travelling waves.     

BIFURCATION OF SINGULAR POINTS NEAR A DOUBLE FOLD POINT INZ_2 -SYMMETRIC NONLINEAR EQUATIONS

We consider the bifurcation of singular points near a double fold point in Z2 -symmetric nonlinear equations with two parameters,where the linearization has a two dimensional null space spanned by a symmetric null vector and an ami-symmetric null vector. In particular, we show the existence of a turning point path and a pitchfork point path passing ihrough the double fold point and they are the only singular points nearby. Their nondegeneracy is confirmed. A supporting numerical example is also provided. The main tools for our analysis as well as the compulation are some extended systems.     

Codimension two bifurcations of fixed points in a class of vibratory systems with symmetrical rigid stops

A vibratory system having symmetrically placed rigid stops and subjected to periodic excitation is considered. Local codimension two bifurcations of the vibratory system with symmetrical rigid stops, associated with double Hopf bifurcation and interaction of Hopf and pitchfork bifurcation, are analyzed by using the center manifold theorem technique and normal form method of maps. Dynamic behavior of the system, near the points of codimension two bifurcations, is investigated by using qualitative analysis and numerical simulation. Hopf-flip bifurcation of fixed points in the vibratory system with a single stop are briefly analyzed by comparison with unfoldings analyses of Hopf-pitchfork bifurcation of the vibratory system with symmetrical rigid stops. Near the value of double Hopf bifurcation there exist period-one double-impact symmetrical motion and quasi-periodic impact motions. The quasi-periodic impact motions are represented by the closed circle and “tire-like” attractor in projected Poincaré sections. With change of system parameters, the quasi-periodic impact motions usually lead to chaos via “tire-like” torus doubling.