92,170 research outputs found
Repeated games for eikonal equations, integral curvature flows and non-linear parabolic integro-differential equations
The main purpose of this paper is to approximate several non-local evolution
equations by zero-sum repeated games in the spirit of the previous works of
Kohn and the second author (2006 and 2009): general fully non-linear parabolic
integro-differential equations on the one hand, and the integral curvature flow
of an interface (Imbert, 2008) on the other hand. In order to do so, we start
by constructing such a game for eikonal equations whose speed has a
non-constant sign. This provides a (discrete) deterministic control
interpretation of these evolution equations. In all our games, two players
choose positions successively, and their final payoff is determined by their
positions and additional parameters of choice. Because of the non-locality of
the problems approximated, by contrast with local problems, their choices have
to "collect" information far from their current position. For integral
curvature flows, players choose hypersurfaces in the whole space and positions
on these hypersurfaces. For parabolic integro-differential equations, players
choose smooth functions on the whole space
A structure-preserving parametric finite element method for area-conserved generalized mean curvature flow
We propose and analyze a structure-preserving parametric finite element
method (SP-PFEM) to simulate the motion of closed curves governed by
area-conserved generalized mean curvature flow in two dimensions (2D). We first
present a variational formulation and rigorously prove that it preserves two
fundamental geometric structures of the flows, i.e., (a) the conservation of
the area enclosed by the closed curve; (b) the decrease of the perimeter of the
curve. Then the variational formulation is approximated by using piecewise
linear parametric finite elements in space to develop the semi-discrete scheme.
With the help of the discrete Cauchy's inequality and discrete power mean
inequality, the area conservation and perimeter decrease properties of the
semi-discrete scheme are shown. On this basis, by combining the backward Euler
method in time and a proper approximation of the unit normal vector, a
structure-preserving fully discrete scheme is constructed successfully, which
can preserve the two essential geometric structures simultaneously at the
discrete level. Finally, numerical experiments test the convergence rate, area
conservation, perimeter decrease and mesh quality, and depict the evolution of
curves. Numerical results indicate that the proposed SP-PFEM provides a
reliable and powerful tool for the simulation of area-conserved generalized
mean curvature flow in 2D.Comment: 24 pages, 8 figure
Volume-preserving mean curvature flow of revolution hypersurfaces in a Rotationally Symmetric Space
In an ambient space with rotational symmetry around an axis (which include
the Hyperbolic and Euclidean spaces), we study the evolution under the
volume-preserving mean curvature flow of a revolution hypersurface M generated
by a graph over the axis of revolution and with boundary in two totally
geodesic hypersurfaces (tgh for short). Requiring that, for each time t, the
evolving hypersurface M_t meets such tgh ortogonally, we prove that: a) the
flow exists while M_t does not touch the axis of rotation; b) throughout the
time interval of existence, b1) the generating curve of M_t remains a graph,
and b2) the averaged mean curvature is double side bounded by positive
constants; c) the singularity set (if non-empty) is finite and discrete along
the axis; d) under a suitable hypothesis relating the enclosed volume to the
n-volume of M, we achieve long time existence and convergence to a revolution
hypersurface of constant mean curvature.Comment: 24 pages. We have added some lines at the beginning explaining the
notation, and clarified a little bit more the proofs of Proposition 1 and
Theorems 5 and 10, the statements of Proposition 2 and Corollary 3 and an
argument in Remark 1. We have also completed reference 18. A version of this
paper will appear in Mathematische Zeitschrif
Gradient flows and a Trotter--Kato formula of semi-convex functions on CAT(1)-spaces
We generalize the theory of gradient flows of semi-convex functions on
CAT(0)-spaces, developed by Mayer and Ambrosio--Gigli--Savar\'e, to
CAT(1)-spaces. The key tool is the so-called "commutativity" representing a
Riemannian nature of the space, and all results hold true also for metric
spaces satisfying the commutativity with semi-convex squared distance
functions. Our approach combining the semi-convexity of the squared distance
function with a Riemannian property of the space seems to be of independent
interest, and can be compared with Savar\'e's work on the local angle condition
under lower curvature bounds. Applications include the convergence of the
discrete variational scheme to a unique gradient curve, the contraction
property and the evolution variational inequality of the gradient flow, and a
Trotter--Kato product formula for pairs of semi-convex functions.Comment: 27 pages; minor revisions; to appear in Amer. J. Mat
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