We study the question whether multistep methods or general multi-value methods can be symplectic. Already a precise understanding of symplecticity of such methods is a nontrivial task, because they advance the numerical solution in a higher dimensional space (in contrast to one-step methods). The essential ingredient for the present study is the formal existence of an invariant manifold, on whi...

On general symplectic manifolds we describe a correspondence between symplectic transformations and their phase functions. On the quantum level, this is a correspondence between unitary operators and phase functions of the WKB-approximation. We represent generic functions via symplectic area of membranes and consider related geometric properties of the noncommutative phase product. An interpret...

The Seiberg-Witten equations are defined on any smooth 4-manifold. By appropriately counting the solutions to the equations, one obtains smooth 4-manifold invariants. On a symplectic 4-manifold, these invariants have a symplectic interpretation, as a count of pseudoholomorphic curves. This allows us to transfer information between the smooth and symplectic categories in four dimensions. In the ...

Conformal symplecticity is generalized to forced-damped multi-symplectic PDEs in 1+1 dimensions. Since a conformal multi-symplectic property has a concise form for these equations, numerical algorithms that preserve this property, from a modified equations point of view, are available. In effect, the modified equations for standard multi-symplectic methods and for space-time splitting methods s...

Symplectic integrators do not, in general, reproduce all the features of the dynamics of the Hamiltonian systems which they approximate. For example, energy conservation is lost, and global features such as separatrices can be destroyed. We study these effects for a Hamiltonian system with a single degree of freedom and the simplest possible symplectic integrator. We look at a sequence of Hamil...

We set S1 = R/2πZ throughout. Let (M,ω) be a symplectic manifold. A symplectic S1-action on (M,ω) is a smooth family ψt ∈ Symp(M,ω), t ∈ S1, such that ψt+s = ψt ◦ ψs for any t, s ∈ S1. One can easily check that the corresponding vector fields Xt ≡ d dtψt ◦ψ −1 t is time-independent, i.e., Xt = X is constant in t. We call X the associated vector field of the given symplectic S1-action. Note that...

A symplectic variety is a normal complex variety X with a holomorphic symplectic form ω on the regular part X reg and with rational Gorenstein sin-gularities. Affine symplectic varieties arise in many different ways such as closures of nilpotent orbits of a complex simple Lie algebra, as Slodowy slices to such nilpotent orbits or as symplectic reductions of holomorphic symplec-tic manifolds wit...

On one side, from the properties of Floer cohomology, invariant associated to a symplectic manifold, we define and study a notion of symplectic hyperbolicity and a symplectic capacity measuring it. On the other side, the usual notions of complex hyperbolicity can be straightforwardly generalized to the case of almost-complex manifolds by using pseudo-holomorphic curves. That’s why we study the ...

We generalize various symplectic reduction techniques of Marsden, Weinstein, Sjamaar, Bates, Lerman, Marle, Kazhdan, Kostant, and Sternberg to the context of the optimal momentum map. We see that, even though all those reduction procedures had been designed to deal with canonical actions on symplectic manifolds in the presence of a momentum map, our construction allows the construction of sympl...

The aim of this text is to give an accessible overview to some recent results concerning contact manifolds and their symplectic fillings. In particular, we work out the weakest compatibility conditions between a symplectic manifold and a contact structure on its boundary to still be able to obtain a sensible theory (Chapter II), furthermore we prove two results (Theorem A and B in Section I.4) ...