The maximal and minimal extensions of an operator defined by a given differential expression on the subspace of functions of compact support. The domains of definition of the maximal and minimal operators can be concretely described in a number of cases, for example, for an ordinary differential operator, for elliptic operators and for differential operators with constant coefficients.
[1] | Yu.M. [Yu.M. Berezanskii] Berezanskiy, "Expansion in eigenfunctions of selfadjoint operators" , Amer. Math. Soc. (1968) (Translated from Russian) |