Positive operators

Аннотация

Positive operators made their debut at the beginning of the nineteenth century. They were tied to integral operators (whose study triggered the birth of functional analysis) and to matrices with nonnegative entries. However, positive operators were investigated in a systematic manner much later. Their study followed closely the development of Riesz spaces. An address of F. Riesz in 1928, "On the decomposition of linear functionals” [166] (into their positive and negative parts), at the International Congress of Mathematicians in Bologna marked the beginnings of the study of Riesz spaces and positive operators.