*2.1. Notation*

The notation used throughout the paper is described next. R is the set of reals, and Z<sup>+</sup> is the set of positive integers. R*<sup>q</sup>* stands for real vectors of dimension *q*. R*p*×*<sup>q</sup>* represents real matrices of dimension *p* × *q*. An identity matrix with *q* rows and *q* columns is denoted by *Iq*. col(*x*1, *x*2) is a vector obtained after stacking column vectors *x*<sup>1</sup> over *x*2. rank(*M*) denotes the rank of matrix *<sup>M</sup>* <sup>∈</sup> <sup>R</sup>*p*×*q*, and colspan(*M*) represents the set of all linear combinations of its column vectors. *σ* denotes the shift operator, which applies to a function *<sup>f</sup>* : <sup>Z</sup><sup>+</sup> <sup>→</sup> <sup>R</sup>*<sup>q</sup>* in the form (*<sup>σ</sup> <sup>f</sup>*)(*t*) :<sup>=</sup> *<sup>f</sup>*(*<sup>t</sup>* <sup>+</sup> <sup>1</sup>). This operator can be extended to an order *N*, as (*σ<sup>N</sup> f*)(*t*) := *f*(*t* + *N*).
