Real and complex interpolation methods for finite and infinite families of Banach spaces

AbstractA comparative study is made of the various interpolation spaces generated with respect to n-tuples or infinite families of compatible Banach spaces by real and complex interpolation methods due to Sparr, Favini-Lions, Coifman-Cwikel-Rochberg-Sagher-Weiss, and Fernandez. Certain inclusions are established between these spaces and examples are given showing that in general they do not coincide. It is also shown that, in contrast to the case of couples of spaces, the spaces generated by the above methods may depend on the structure of the containing space in which the Banach spaces of the n-tuple (nϵ 3) or infinite family are embedded. Finally a construction is given which enables the spaces of Sparr and Favini-Lions, hitherto defined only with respect to n-tuples, to also be defined with respect to infinite families of Banach spaces