The interplay between Dirac systems, Morse families and Interconnection

On certain analytical methods in finding integrable systems and their interconnections

In this paper, to begin with, we review six different analytical methods which are widely used to derive symmetries, integrating factors, multipliers, Darboux polynomials and integrals of second order nonlinear ordinary differential equations. We illustrate the algorithm behind each method by considering a nonlinear oscillator equation as an example. In the second part of this paper, we examine the interconnections between these methods. We establish a road map between extended Prelle-Singer procedure with all other methods cited above and thereby demonstrate the interplay between Lie point sy…

Interplay Between Approximation Theory and Renormalization Group

The review presents general methods for treating complicated problems that cannot be solved exactly and whose solution encounters two major difficulties. First, there are no small parameters allowing for the safe use of perturbation theory in powers of these parameters, and even when small parameters exist, the related perturbative series are strongly divergent. Second, such perturbative series in powers of these parameters are rather short, so that the standard resummation techniques either yield bad approximations or are not applicable at all. The emphasis in the review is on the methods adv…

Riccati、Ermakov 与 Schrödinger 方程之间的相互作用以产生具有实能谱的复值势

Interplay between Riccati, Ermakov and Schroedinger equations to produce complex-valued potentials with real energy spectrum

本文利用 Riccati 与 Ermakov 方程结合 Darboux 方法，构造能谱继承 Hermitian 可解系统全部能量且额外含一个实本征值且无奇点的复值势，并以 Morse 和三角 Pöschl-Teller 势为例说明。