Calcul différentiel et intégral adapté aux substitutions par Volterra

Abstract

In 1887 Volterra was in search of a general vision for analysis. His most famous work led him to the definition of functionals, or more precisely to develop a differential and integral calculus for “functions that depend on other functions” or “line functions.”However, Volterra's efforts to define a general context for certain analytical problems would also lead him to extend the notions of derivation and integration to substitutions—matrices whose coefficients are functions—which have an important role in the study of differential linear equations.In a memoir entitled Sui fondamenti della teoria delle equazioni differenziali lineari Volterra establishes a differential and integral calculus for substitutions. This work, which allows one to think of linear differential equations through two operations on substitutions—derivation and integration, also makes it possible to analyse the progression strategy implemented by the Italian mathematician in his search for a generalized analysis from the beginning of his career.We are examining the selection and reorganization processes that have enabled Volterra to transpose a well-established theory for ordinary functions to a framework adapted to substitutions. We thus reveal a dynamic of progress towards generality, and explore the elements on which his thoughts are based.Far from being an anecdotal, this text, which does not solve any conjecture, allows us to see a coherence in Volterra's way of progressing, and clarifies his role in the search for an analysis which would gradually become the functional analysis of the 20th century.