© 1993 by British Computer Society
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On the Complexity of Quantifier Elimination: the Structural Approach
Universitat Pompeu Fabra, c/ Balmes 132, Barcelona 08008, Spain
The aim of this paper is to survey certain theoretical aspects of the complexity of quantifier elimination in the elementary theory of the real numbers with real constants, and to present some new results on the subject. We use the new model of computation introduced by L. Blum, M. Shub and S. Smale that accepts as inputs vectors of real numbers and allows the transfer of the structural approach to computability and complexity for computations with real numbers. More concretely, we give a proof of the existence of NPR-complete problems. Also, we introduce a new complexity class PATR which describes the complexity of the decision of quantified formulae and, in order to study its relationship with the already existing complexity classes, a model for parallel computations is also introduced. Using the classes resulting by bounding resources in this parallel model, some separation results are finally obtained. In particular, we show that the polynomial hierarchy overs the reals is strictly contained in PATR.
Received December 1992. revised April 1993.
* Partially supported by the ESPRIT BRA Programs of the EC n. 7141 and 6546, projects ALCOM II and PROMotion, and DGICyT PB 89/0379.
Universitat Pompeu Fabra, c/ Balmes 132, Barcelona 08008, Spain