Generalized nonlinear oscillators with quasi-harmonic behaviour:   classical solutions
  The classical nonlinear oscillator, proposed by Mathews and Lakshmanan in 1974 and including a position-dependent mass in the kinetic energy term, is generalized in two different ways by adding an extra term to the potential. The solutions of the Euler-Lagrange equation are shown to exhibit richer behaviour patterns than those of the original nonlinear oscillator. 
C. Quesne
math-ph math.MP nlin.SI physics.class-ph