“…Along with extensive applications of Legendre and Chebyshev spectral methods for bounded domains (cf. [1,2,6,9,11,12]), considerable progress has been made recently in spectral methods for unbounded domains. Among these methods, a direct and commonly used approach is based on certain orthogonal approximations on infinite intervals, i.e., the Hermite and Laguerre spectral methods ( see, e.g., [5,10,13,16,18,23,24,28,32]).…”