José Félix Costa

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In this paper we show that Shannon’s General Purpose Analog Computer (GPAC) is equivalent to a particular class of recursive functions over the reals with the flavour of Kleene’s classical recursive function theory. We first consider the GPAC and several of its extensions to show that all these models have drawbacks and we introduce an alternative(More)
Shannon's General Purpose Analog Computer (GPAC) is an elegant model of analog computation in continuous time. In this paper, we consider whether the set G of GPAC-computable functions is closed under iteration, that is, whether for any function f(x) 2 G there is a function F (x; t) 2 G such that F (x; t) = f (x) for non-negative integers t. We show that G(More)
We discuss combining physical experiments with machine computations and introduce a form of analogue-digital Turing machine. We examine in detail a case study where an experimental procedure based on Newtonian kinematics is combined with a class of Turing machines. Three forms of analogue-digital machine are studied, in which physical parameters can be set(More)
In the last years, recursive functions over the reals (Theoret. Comput. Sci. 162 (1996) 23) have been 9 considered, first as a model of analog computation, and second to obtain analog characterizations of classical computational complexity classes (Unconventional Models of Computation, UMC 2002, 11 Lecture Notes in Computer Science, Vol. 2509, Springer,(More)
The class of recursive functions over the reals, denoted by REC(R), was introduced by Cristopher Moore in his seminal paper written in 1995. Since then many subsequent investigations brought new results: the class REC(R) was put in relation with the class of functions generated by the General Purpose Analogue Computer of Claude Shannon; classical digital(More)
A categorial semantic domain for objects is presented in order to clarify both aggregation and specialization. Three kinds of specialization are discussed: (1) subtyping (specialization with no side effects and no non-monotonic overriding); (2) monotonic specialization (possibly with side effects but still only with monotonic overriding); and (3)(More)