In the complex case, differentiability is understood in the sense that the real and complex parts must be differentiable, as discussed in the Appendix on differentials, and linearizations could be computed for the real system of twice the dimension associated to any given system over B.
Definition 2.5.2 Let Q be a W discrete-time system over W, and assume that E is a trajectory for R on an interval T.
The linearization of Y along U is the discrete-time linear system O with local-in-time description P, where L.
If P is a system with outputs, then O is the discrete-time linear system with outputs having the above U, Y, and the readout map T.