Nearest-neighbour level spacings for the non-periodic discrete nonlinear Schrodinger equation

The phase space of the classical non-periodic discrete nonlinear Schrodinger equation contains both a chaotic region and a continuous family of periodic orbits. In a bid to determine the extent to which this mixed behaviour manifests itself in the transition to quantum mechanics, we study the nearest-neighbour level-spacing distribution of the corresponding quantum energy levels. This is compared with the optimal Berry-Robnik and Brody distributions, which continuously interpolate between regular and chaotic level spacing statistics.