ABSTRACT
The rest of the book is devoted to a study of some partial differential operators with variable coefficients. As in preceding chapters, the emphasis is on important operators arising in physics. We begin in this chapter with the Hermite operator, which is a mathematical model in physics. First we give a recall without proofs of the basic properties of Hermite functions that we need in this chapter and to some extent the following chapters. The books [34, 40] are useful references.
