We define a class, denoted APP, of real-valued functions f : {0, 1}n → [0, 1] such that f can be approximated to within any > 0 by a probabilistic Turing machine running in time poly(n, 1/ ). The class APP can be viewed as a generalization of BPP. We argue that APP is more natural and more important than BPP, and that most results about BPP are better stated as results about APP. We show that A...

A fading-memory system is a system that tends to forget its input asymptotically over time. It has been shown that discrete-time fading-memory systems can be uniformly approximated arbitrarily closely over a set of bounded input sequences simply by uniformly approximating sufficiently closely either the external or internal representation of the system. In other words, the problem of uniformly ...

It is known that the space of real valued, continuous functions C(B) over a multidimensional compact domain B ⊂ R , k ≥ 2 does not admit Haar spaces, which means that interpolation problems in finite dimensional subspaces V of C(B) may not have a solutions in C(B). The corresponding standard short and elegant proof does not apply to complex valued functions over B ⊂ C. Nevertheless, in this sit...