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Commutators and linearizations of isochronous centers

Luisa Mazzi, Marco Sabatini (2000)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We study isochronous centers of some classes of plane differential systems. We consider systems with constant angular speed, both with homogeneous and nonhomogenous nonlinearities. We show how to construct linearizations and first integrals of such systems, if a commutator is known. Commutators are found for some classes of systems. The results obtained are used to prove the isochronicity of some classes of centers, and to find first integrals for a class of Liénard equations with isochronous centers....

Compact perturbations of linear differential equations in locally convex spaces

S. A. Shkarin (2006)

Studia Mathematica

Herzog and Lemmert have proven that if E is a Fréchet space and T: E → E is a continuous linear operator, then solvability (in [0,1]) of the Cauchy problem ẋ = Tx, x(0) = x₀ for any x₀ ∈ E implies solvability of the problem ẋ(t) = Tx(t) + f(t,x(t)), x(0) = x₀ for any x₀ ∈ E and any continuous map f: [0,1] × E → E with relatively compact image. We prove the same theorem for a large class of locally convex spaces including: • DFS-spaces, i.e., strong duals of Fréchet-Schwartz spaces,...

Comparison theorems for differential equations of neutral type

Miroslava Růžičková (1997)

Mathematica Bohemica

We are interested in comparing the oscillatory and asymptotic properties of the equations L n [ x ( t ) - P ( t ) x ( g ( t ) ) ] + δ f ( t , x ( h ( t ) ) ) = 0 with those of the equations M n [ x ( t ) - P ( t ) x ( g ( t ) ) ] + δ Q ( t ) q ( x ( r ( t ) ) ) = 0 .

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