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The computation of coefficients of amplitude systems for Turing bifurcations is a straightforward but sometimes elaborate task, in particular for 2D or 3D wave vector lattices. The Matlab tool ampsys automates such computations for two classes of problems, namely scalar equations of Swift-Hohenberg type and generalizations, and reaction-diffusion systems with an arbitrary number of components. The tool is designed to require minimal user input, and for a number of cases can also deal with symbolic computations. After a brief review of the setup of amplitude systems we explain the tool by a number of 1D, 2D and 3D examples over various wave vector lattices.
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We explain some pde2path setups for pattern formation in 1D, 2D and 3D. A focus is on new pde2path functions for branch switching at steady bifurcation points of higher multiplicity, typically due to discrete symmetries, but we also review general concepts of pattern formation and their handling in pde2path, including localized patterns and homoclinic snaking, again in 1D, 2D and 3D, based on the demo sh (Swift-Hohenberg equation). Next, the demos schnakpat (a Schnakenberg reaction-diffusion system) and chemtax (a quasilinear RD system with cross-diffusion from chemotaxis) simplify and unify previous results in a simple and concise way, CH (Cahn-Hilliard) deals with mass constraints, hexex deals with (multiple) branch points of higher degeneracy in a scalar problem on a hexagonal domain, and shgc illustrates some global coupling. The demos acS, actor, schnakS and schnaktor (the Allen-Cahn and Schnakenberg models on spheres and tori) consider pattern formation on curved surfaces, cpol considers a problem of cell polarization described by bulk-surface coupling, and bruosc (Brusselator) explains how to augment autonomous systems by a time periodic forcing. Along the way we also comment on the choice of meshes and mesh adaptation, on time integration, and we give some examples of branch point continuation and Hopf point continuation to approximate stability boundaries.
We explain the setup for using the pde2path libraries for Hopf bifurcation and continuation of branches of periodic orbits and give implementation details of the associated demo directories. See [Uecker, Comm. in Comp. Phys., 2019] for a description of the basic algorithms and the mathematical background of the examples. Additionally we explain the treatment of Hopf bifurcations in systems with continuous symmetries, including the continuation of traveling waves and rotating waves in O(2) equivariant systems as relative equilibria, the continuation of Hopf bifurcation points via extended systems, and some simple setups for the bifurcation from periodic orbits associated to critical Floquet multipliers going through +-1.
Stability of cylindrical and spherical crystals growing from a supersaturated solution (in Mullins-Sekerkas approximation) is considered using the maximum entropy production principle. The concept of the binodal of the nonequilibrium (morphological) phase transition is introduced for interpretation of the obtained results. The limits of the metastable regions are determined. The morphological phase diagrams of stable-unstable growth in the plane (surface energy, supersaturation) are given.
The localization characters of the first-order rogue wave (RW) solution $u$ of the Kundu-Eckhaus equation is studied in this paper. We discover a full process of the evolution for the contour line with height $c^2+d$ along the orthogonal direction of the ($t,x$)-plane for a first-order RW $|u|^2$: A point at height $9c^2$ generates a convex curve for $3c^2leq d<8c^2$, whereas it becomes a concave curve for $0<d<3c^2$, next it reduces to a hyperbola on asymptotic plane (i.e. equivalently $d=0$), and the two branches of the hyperbola become two separate convex curves when $-c^2<d<0$, and finally they reduce to two separate points at $d=-c^2$. Using the contour line method, the length, width, and area of the RW at height $c^2+d (0<d<8c^2)$ , i.e. above the asymptotic plane, are defined. We study the evolutions of three above-mentioned localization characters on $d$ through analytical and visual methods. The phase difference between the Kundu-Eckhaus and the nonlinear Schrodinger equation is also given by an explicit formula.
The study of nonlinear waves that collapse in finite time is a theme of universal interest, e.g. within optical, atomic, plasma physics, and nonlinear dynamics. Here we revisit the quintessential example of the nonlinear Schrodinger equation and systematically derive a normal form for the emergence of blowup solutions from stationary ones. While this is an extensively studied problem, such a normal form, based on the methodology of asymptotics beyond all algebraic orders, unifies both the dimension-dependent and power-law-dependent bifurcations previously studied; it yields excellent agreement with numerics in both leading and higher-order effects; it is applicable to both infinite and finite domains; and it is valid in all (subcritical, critical and supercritical) regimes.
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