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The purpose of this paper is to give a short self-contained proof of the center-manifold theorem for maps and vector fields in finite-dimensional spaces using the graph transform. In particular, regularity of the center manifold is established using a direct argument that is based on the closedness of sets of differentiable functions whose highest derivatives are Lipschitz continuous in the space of continuous functions; this argument avoids the fiber contraction theorem that is commonly used in this context. [ABSTRACT FROM AUTHOR]

Equation-free modeling aims at extracting low-dimensional macroscopic dynamics from complex high-dimensional systems that govern the evolution of microscopic states. This algorithm relies on lifting and restriction operators that map macroscopic states to microscopic states and vice versa. Combined with simulations of the microscopic state, this algorithm can be used to apply Newton solvers to the implicitly defined low-dimensional macroscopic system or solve it more efficiently using direct numerical simulations. The key challenge is the construction of the lifting and restrictions operators that usually require a priori insight into the underlying application. In this paper, we design an application-independent algorithm that uses diffusion maps to construct these operators from simulation data. Code is available at https://doi.org/10.5281/zenodo.5793299. [ABSTRACT FROM AUTHOR]

We analyze the bifurcation diagrams of spatially localized stationary patterns that exhibit a long spatially periodic interior plateau (referred to as localized rolls). In a wide variety of contexts, these bifurcation diagrams consist of isolas or of intertwined s-shaped curves that are commonly referred to as snaking branches. These diagrams have been rigorously analyzed by connecting the existence curves of localized rolls with the bifurcation structure of fronts that connect the rolls to the trivial state. Previous work assumed that the stable and unstable manifolds of rolls were orientable. Here, we extend these results to the nonorientable case and also discuss topological barriers that prevent snaking, thus allowing only isolas to occur. The results are applied to the Swift–Hohenberg system for which we show that nonorientable roll patterns cannot snake. [ABSTRACT FROM AUTHOR]