Closed characteristics on singular energy levels of second-order Lagrangian systems

We provide a lower bound on the number of closed characteristics on singular energy levels of second-order Lagrangian systems in the presence of saddle-focus equilibria. The hypotheses on the Lagrangian are mild, and the bound is given in terms of the number of saddle-foci and a potential function determined by the Lagrangian. The method of proof is variational, combining techniques to minimize near a saddle-focus and an analog of the method of broken geodesics.     

On Anosov energy levels of convex Hamiltonian systems

Supported by the Max-Planck-Institut für Mathematik and by a travel grant from CDE. On leave from: IMERL-Facultad de Ingenieria, Julio Herrera y Reissig 565, Montevideo-Uruguay     

Note on a general Palais-Smale condition

In this paper, we establish a qualitative deformation theorem for a locally Lipschitz function satisfying a general Palais-Smale type condition. Then we show that, with some assumptions, this compactness condition implies the coercivity of the function.     

Bounded and almost periodic solutions of convex Lagrangian systems

We study some properties of bounded and almost periodic solutions of convex Lagrangian systems in the presence of almost periodic forcing

     

Global surfaces of section in non-regular convex energy levels of Hamiltonian systems

In this paper we prove the existence of global sections of disk-type in non-regular and strictly convex energy levels of integrable and near-integrable Hamiltonian systems with two degrees of freedom. This extends a result of (Hofer et al. in Ann. Math.(2) 148(1):197–289, 1998) where the same statement is true provided the energy level is regular.     

A linear perturbed Palais-Smale condition for lower semicontinuous functions on Banach spaces

This paper introduces a notion of linear perturbed Palais-Smale condition for real-valued functions on Banach spaces. In terms of strongly exposed points, it presents a characterization which guarantees linear perturbed Palais-Smale condition holds for lower semicontinuous functions with bounded effective domains defined on a Banach space with the Radon-Nikody＇m property; and gives an example showing that linear perturbed P-S condition is strictly weaker than the P-S condition.     

Global hyperbolicity and Palais-Smale condition for action functionals in stationary spacetimes

In order to apply variational methods to the action functional for geodesics of a stationary spacetime, some hypotheses, useful to obtain classical Palais-Smale condition, are commonly used: pseudo-coercivity, bounds on certain coefficients of the metric, etc. We prove that these technical assumptions admit a natural interpretation for the conformal structure (causality) of the manifold. As a consequence, any stationary spacetime with a complete timelike Killing vector field and a complete Cauchy hypersurface (thus, globally hyperbolic), is proved to be geodesically connected.     

Generalized and classical almost periodic solutions of Lagrangian systems convex on a compact set

By using the variational method, we establish sufficient conditions for the existence of generalized Besicovitch almost (quasi)periodic solutions and classical quasiperiodic solutions of natural Lagrangian systems with force functions convex on a compact set. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 12, pp. 1601–1608, December, 1998.     

Second-order dynamical systems of Lagrangian type with dissipation

We give a coordinate-independent version of the smallest set of necessary and sufficient conditions for a given system of second-order ordinary differential equations to be of Lagrangian form with additional dissipative forces.     

Perturbation analysis of a condition number for convex inequality systems and global error bounds for analytic systems

In this paper several types of perturbations on a convex inequality system are considered, and conditions are obtained for the system to be well-conditioned under these types of perturbations, where the well-conditionedness of a convex inequality system is defined in terms of the uniform boundedness of condition numbers under a set of perturbations. It is shown that certain types of perturbations can be used to characterize the well-conditionedness of a convex inequality system, in which either the system has a bounded solution set and satisfies the Slater condition or an associated convex inequality system, which defines the recession cone of the solution set for the system, satisfies the Slater condition. Finally, sufficient conditions are given for the existence of a global error bound for an analytic system. It is shown that such a global error bound always holds for any inequality system defined by finitely many convex analytic functions when the zero vector is in the relative interior of the domain of an associated convex conjugate function.     

Regularity for convex viscosity solutions of special Lagrangian equation

We establish interior regularity for convex viscosity solutions of the special Lagrangian equation. Our result states that all such solutions are real analytic in the interior of the domain.     

A generalized finite type condition for iterated function systems

We study iterated function systems (IFSs) of contractive similitudes on Rd with overlaps. We introduce a generalized finite type condition which extends a more restrictive condition in [S.-M. Ngai, Y. Wang, Hausdorff dimension of self-similar sets with overlaps, J. London Math. Soc. (2) 63 (3) (2001) 655-672] and allows us to include some IFSs of contractive similitudes whose contraction ratios are not exponentially commensurable. We show that the generalized finite type condition implies the weak separation property. Under this condition, we can identify the attractor of the IFS with that of a graph-directed IFS, and by modifying a setup of Mauldin and Williams [R.D. Mauldin, S.C. Williams, Hausdorff dimension in graph directed constructions, Trans. Amer. Math. Soc. 309 (1988) 811-829], we can compute the Hausdorff dimension of the attractor in terms of the spectral radius of certain weighted incidence matrix.     

A limiting Lagrangian for infinitely constrained convex optimization inR n

For convex optimization inR ⁿ,we show how a minor modification of the usual Lagrangian function (unlike that of the augmented Lagrangians), plus a limiting operation, allows one to close duality gaps even in the absence of a Kuhn-Tucker vector [see the introductory discussion, and see the discussion in Section 4 regarding Eq. (2)]. The cardinality of the convex constraining functions can be arbitrary (finite, countable, or uncountable).In fact, our main result (Theorem 4.3) reveals much finer detail concerning our limiting Lagrangian. There are affine minorants (for any value 0<1 of the limiting parameter ) of the given convex functions, plus an affine form nonpositive onK, for which a general linear inequality holds onR ⁿAfter substantial weakening, this inequality leads to the conclusions of the previous paragraph.This work is motivated by, and is a direct outgrowth of, research carried out jointly with R. J. Duffin.This research was supported by NSF Grant No. GP-37510X1 and ONR Contract No. N00014-75-C0621, NR-047-048. This paper was presented at Constructive Approaches to Mathematical Models, a symposium in honor of R. J. Duffin, Pittsburgh, Pennsylvania, 1978. The author is grateful to Professor Duffin for discussions relating to the work reported here.The author wishes to thank R. J. Duffin for reading an earlier version of this paper and making numerous suggestions for improving it, which are incorporated here. Our exposition and proofs have profited from comments of C. E. Blair and J. Borwein.     

Adaptive inexact fast augmented Lagrangian methods for constrained convex optimization

In this paper we study two inexact fast augmented Lagrangian algorithms for solving linearly constrained convex optimization problems. Our methods rely on a combination of the excessive-gap-like smoothing technique introduced in Nesterov (SIAM J Optim 16(1):235–249, 2005) and the general inexact oracle framework studied in Devolder (Math Program 146:37–75, 2014). We develop and analyze two augmented based algorithmic instances with constant and adaptive smoothness parameters, and derive a total computational complexity estimate in terms of projections on a simple primal feasible set for each algorithm. For the constant parameter algorithm we obtain the overall computational complexity of order \(\mathcal {O}(\frac{1}{\epsilon ^{5/4}})\), while for the adaptive one we obtain \(\mathcal {O}(\frac{1}{\epsilon })\) total number of projections onto the primal feasible set in order to achieve an \(\epsilon \)-optimal solution for the original problem.     

A second-order Lagrangian condition for restricted control problems

We derive a second-order condition for optimal control problems defined by ordinary differential equations with time-varyingconvex restrictions on controls and with endpoint constraints. This condition generalizes theaccessory minimum problem of the calculus of variations.This research was partially supported by Grant No. MCS 76-06756 of the National Science Foundation.     

The Conley conjecture for Hamiltonian systems on the cotangent bundle and its analogue for Lagrangian systems

In this paper, the Conley conjecture, which was recently proved by Franks and Handel [J. Franks, M. Handel, Periodic points of Hamiltonian surface diffeomorphism, Geom. Topol. 7 (2003) 713-756] (for surfaces of positive genus), Hingston [N. Hingston, Subharmonic solutions of Hamiltonian equations on tori, Ann. Math., in press] (for tori) and Ginzburg [V.L. Ginzburg, The Conley conjecture, arXiv: math.SG/0610956v1] (for closed symplectically aspherical manifolds), is proved for C¹-Hamiltonian systems on the cotangent bundle of a C³-smooth compact manifold M without boundary, of a time 1-periodic C²-smooth Hamiltonian H:R×T^*M→R which is strongly convex and has quadratic growth on the fibers. Namely, we show that such a Hamiltonian system has an infinite sequence of contractible integral periodic solutions such that any one of them cannot be obtained from others by iterations. If H also satisfies H(−t,q,−p)=H(t,q,p) for any (t,q,p)∈R×T^*M, it is shown that the time-1-map of the Hamiltonian system (if exists) has infinitely many periodic points siting in the zero section of T^*M. If M is C⁵-smooth and dimM>1, H is of C⁴ class and independent of time t, then for any τ>0 the corresponding system has an infinite sequence of contractible periodic solutions of periods of integral multiple of τ such that any one of them cannot be obtained from others by iterations or rotations. These results are obtained by proving similar results for the Lagrangian system of the Fenchel transform of H, L:R×TM→R, which is proved to be strongly convex and to have quadratic growth in the velocities yet.     

A Gauss-Seidel type solver for special convex programs,with application to frictional contact mechanics

An iterative method is described that solves the constrained minimization of a convex function, when the constraintsg _j(x ₁,...,x _n)0 are functions of only a few variables and can be partitioned in some way. A proof of convergence is given which is based on the fact that the function values that are generated decrease. The relation to the nonlinear equation solver TanGS is shown (Ref. 1), together with some new results for TanGS. Finally, the solver is applied to the solution of tangential traction in contact mechanics.