Abstract

The standard way to study a compound singularity is to decompose it into the simpler ones using either blow up techniques or appropriate deformations. Among deformations, one distinguishes between miniversal deformations (related to deformations of a basis of the local algebra of singularity) and good deformations (one-parameter deformations with simple singularities coalescing into a multiple one). In concrete settings, explicit construction of a good deformation is an art rather than a science. In this paper, we discuss some cases important from the application viewpoint when explicit good deformations can be constructed and effectively used. Our applications include: (a) an $ n $-dimensional Euler-Jacobi formula with simple and double roots, and (b) a simple approach to the known classification of phase portraits of planar differential systems around linearly non-zero equilibrium.

Highlights

  • The restrictions on possible values of the determinants are given by the Euler-Jacobi formula which is both elegant and effective for the applications

  • In a parallel way, according to the Grobman-Hartman Theorem, the local behavior of a differential system near a hyperbolic equilibrium is equivalent to the behavior of the linearized system at the equilibrium

  • The standard theoretical method allowing one to attack both problems is known under the wordings resolution of singularity/desingularization: under an appropriate transformation/deformation of the given map, one decomposes a compound singularity into the simpler ones. Practical implementation of this method may be based on the usage of blow up techniques, miniversal deformations, good deformations, to mention a few

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Summary

Introduction

The standard theoretical method allowing one (at least, theoretically) to attack both problems is known under the wordings resolution of singularity/desingularization: under an appropriate transformation/deformation of the given map, one decomposes a compound singularity into the simpler ones Practical implementation of this method may be based on the usage of blow up techniques (a change of variables on a deleted neighborhood, see [10, 12, 13, 22, 25]), miniversal deformations (for example, unfoldings related to deformations of a basis of the local algebra of singularity, see [9, 7, 8]), good deformations (one-parameter deformations with simple singularities coalescing into a multiple one, see [18]), to mention a few.

Euler-Jacobi formula
Good deformations
Application
Apply the following rules:
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