Off-diagonal matrix extrapolation for Muckenhoupt bases

In this paper we extend the theory of Rubio de Francia extrapolation for matrix weights, recently introduced by Bownik and the first author (2022), to off-diagonal extrapolation. We also show that the theory of matrix weighted extrapolation can be extended to matrix \(A_p\) classes defined with respect to a general basis, provided that a version of the Christ–Goldberg maximal operator is assumed to be bounded. Finally, we extend a recent result by Vuorinen (2024) and show that all of the multiparameter bases have this property.