Interpolation Functors In Weak-Type Interpolation

For interpolation in the diagonal case, i.e. with respect to the two couples (X, X) and (Y, Y), there exists a natural relation between weak-type and strong-type interpolation. Indeed, weak-type interpolation is related to the “M-couples” (ΛX, MX) and (ΛY, MY) of the Lorentz spaces of X and Y. Since ΛZ ⊂ MZ for any space Z, any weak-type interpolation space also has the (strong-type) interpolation property for the “Λ-couples” (ΛX, ΛX) and (ΛY, ΛY). In this paper a scale Gc, c > 0,of interpolation functors with respect to the Λ-couples is introduced such that all generated interpolation spaces (also) have the weak-type interpolation property. Moreover, we will show that a space is a weak interpolation space if and only if it is generated by one of these functors. © 1997, Birkhäuser Verlag, Basel.