Nontrivial solvability of elliptic equations in divergence form with complex coefficients

The stationary Fokker-Planck-Kolmogorov equation with complex diffusion coefficients and a complex vector-field is examined on a torus. Under suitable conditions for the diffusion coefficients, it is proven that a nontrivial solution exists and the solution space is multidimensional in some cases.     

Unique solvability of the stationary Fokker-Planck equation in a class of positive functions

We study the stationary Focker-Planck equation Δu ? div(u f) = 0 with a given vector field f of the class C ₀ ^∞ (R ⁿ ) on the basis of a fixed point principle that generalizes the contraction mapping method. Next, we introduce a parameter in the equation and prove the unique solvability of the equation Δu ? div(uγ f) = 0 with the parameter in the class of positive slowly increasing functions. We reveal the analytic dependence of the positive solution u on the parameter γ. Pointwise estimates for positive solutions are proved.     

Existence and nonuniqueness of solutions to a functional-differential equation

We examine the functional-differential equation Δu(x) — div(u(H(x))f (x)) = 0 on a torus which is a generalization of the stationary Fokker-Planck equation. Under sufficiently general assumptions on the vector field f and the map H, we prove the existence of a nontrivial solution. In some cases the subspace of solutions is established to be multidimensional.     

On the substantiation of a projection method for the stationary Fokker-Planck equation

A projection-type condition is discussed that is sufficient for the stationary Fokker-Planck equation Δu - div(u f) = 0 to be solvable within a class of probability density functions. Based on existence theorems and estimates of positive solutions obtained by the author, a fairly large class of vector fields f satisfying this condition is proposed.     

Stationary Fokker–Planck equation on noncompact manifolds and in unbounded domains

We investigate the Fokker–Planck equation on an infinite cylindrical surface and in an infinite strip with reflecting boundary conditions, prove the existence of a positive (not necessarily integrable) solution, and derive various conditions on the vector field f that are sufficient for the existence of a solution that is the probability density. In particular, these conditions are satisfied for some vector fields f with integral trajectories going to infinity.     

On the Correct Determination of Flow of a Discontinuous Solenoidal Vector Field

Ukrainian Mathematical Journal - We prove inequalities connecting a flow through the (n?1)-dimensional surface S of a smooth solenoidal vector field with its Lp(U)-norm (U is an n-dimensional...     

Numerical stabilization of the Lorenz system by a small external perturbation

The Lorenz system perturbed by noise and its invariant measure whose density obeys the stationary Fokker-Planck equation are analyzed numerically. A linear functional of the invariant measure is considered, and its variation caused by a variation in the right-hand side of the Lorenz system is calculated. A small (in modulus) external perturbation is calculated under which the strange attractor of the Lorenz system degenerates into a stable fixed point.