1,136 research outputs found
Stabilization of Unstable Procedures: The Recursive Projection Method
Fixed-point iterative procedures for solving nonlinear parameter dependent problems can converge for some interval of parameter values and diverge as the parameter changes. The Recursive Projection Method (RPM), which stabilizes such procedures by computing a projection onto the unstable subspace is presented. On this subspace a Newton or special Newton iteration is performed, and the fixed-point iteration is used on the complement. As continuation in the parameter proceeds, the projection is efficiently updated, possibly increasing or decreasing the dimension of the unstable subspace. The method is extremely effective when the dimension of the unstable subspace is small compared to the dimension of the system. Convergence proofs are given and pseudo-arclength continuation on the unstable subspace is introduced to allow continuation past folds. Examples are presented for an important application of the RPM in which a “black-box” time integration scheme is stabilized, enabling it to compute unstable steady states. The RPM can also be used to accelerate iterative procedures when slow convergence is due to a few slowly decaying modes
Symmetries in the Lorenz-96 model
The Lorenz-96 model is widely used as a test model for various applications,
such as data assimilation methods. This symmetric model has the forcing
and the dimension as parameters and is
equivariant. In this paper, we unravel its dynamics for
using equivariant bifurcation theory. Symmetry gives rise to invariant
subspaces, that play an important role in this model. We exploit them in order
to generalise results from a low dimension to all multiples of that dimension.
We discuss symmetry for periodic orbits as well.
Our analysis leads to proofs of the existence of pitchfork bifurcations for
in specific dimensions : In all even dimensions, the equilibrium
exhibits a supercritical pitchfork bifurcation. In dimensions
, , a second supercritical pitchfork bifurcation occurs
simultaneously for both equilibria originating from the previous one.
Furthermore, numerical observations reveal that in dimension , where
and is odd, there is a finite cascade of exactly
subsequent pitchfork bifurcations, whose bifurcation values are independent
of . This structure is discussed and interpreted in light of the symmetries
of the model.Comment: 31 pages, 9 figures and 3 table
Qualitative Analysis of the Classical and Quantum Manakov Top
Qualitative features of the Manakov top are discussed for the classical and
quantum versions of the problem. Energy-momentum diagram for this integrable
classical problem and quantum joint spectrum of two commuting observables for
associated quantum problem are analyzed. It is demonstrated that the evolution
of the specially chosen quantum cell through the joint quantum spectrum can be
defined for paths which cross singular strata. The corresponding quantum
monodromy transformation is introduced.Comment: This is a contribution to the Vadim Kuznetsov Memorial Issue on
Integrable Systems and Related Topics, published in SIGMA (Symmetry,
Integrability and Geometry: Methods and Applications) at
http://www.emis.de/journals/SIGMA
Pattern formation for the Swift-Hohenberg equation on the hyperbolic plane
We present an overview of pattern formation analysis for an analogue of the
Swift-Hohenberg equation posed on the real hyperbolic space of dimension two,
which we identify with the Poincar\'e disc D. Different types of patterns are
considered: spatially periodic stationary solutions, radial solutions and
traveling waves, however there are significant differences in the results with
the Euclidean case. We apply equivariant bifurcation theory to the study of
spatially periodic solutions on a given lattice of D also called H-planforms in
reference with the "planforms" introduced for pattern formation in Euclidean
space. We consider in details the case of the regular octagonal lattice and
give a complete descriptions of all H-planforms bifurcating in this case. For
radial solutions (in geodesic polar coordinates), we present a result of
existence for stationary localized radial solutions, which we have adapted from
techniques on the Euclidean plane. Finally, we show that unlike the Euclidean
case, the Swift-Hohenberg equation in the hyperbolic plane undergoes a Hopf
bifurcation to traveling waves which are invariant along horocycles of D and
periodic in the "transverse" direction. We highlight our theoretical results
with a selection of numerical simulations.Comment: Dedicated to Klaus Kirchg\"assne
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