Now showing items 1-11 of 11

    • A combinatorial technique for separating counting complexity classes 

      Torán Romero, Jacobo (1988)
      External research report
      Open Access
      We introduce a new combinatorial technique to obtain relativized separations of certain complexity classes related to the idea of counting, like PP, G (exact counting), and ¿P (parity). To demonstrate its usefulness we ...
    • Classes of bounded nondeterminism 

      Díaz Cort, Josep; Torán Romero, Jacobo (1988)
      External research report
      Open Access
      We study certain language classes located between P and N P that are defined by polynomial time machines with a bounded amount of nondeterminism. We observe that these classes have complete problems and find a characterization ...
    • Computing functions with parallel queries to NP 

      Jenner Núñez, Birgit; Torán Romero, Jacobo (1993-03)
      External research report
      Open Access
      The class "Theta_2^p" of languages polynomial time truth-table reducible to sets in NP has a wide range of different characterizations. We survey some of them studying the classes obtained when the characterizations are ...
    • Kolmogorov complexity of #P functions 

      Green, Frederic; Torán Romero, Jacobo (1991-01)
      External research report
      Open Access
      Are the outputs of #P functions "random"? We way phrase this question more precisely: are there #P functions whose outputs cannot in general be compressed into a string of small length, and recovered quickly from that ...
    • On the expected depth of boolean circuits 

      Díaz Cort, Josep; Serna Iglesias, María José; Spirakis, Paul George; Torán Romero, Jacobo (1994-02)
      External research report
      Open Access
      In this paper we analyze the expected depth of a circuit randomly generated from a uniform model. We show that the expected depth of such circuits is polylogarithmic in the number of gates. This result allows us to place ...
    • Parallel approximation schemes for problems on planar graphs 

      Díaz Cort, Josep; Serna Iglesias, María José; Torán Romero, Jacobo (1993-03)
      External research report
      Open Access
      This paper describes a technique to obtain NC approximation schemes for the Maximum Independent Set in planar graphs and related optimization problems.
    • Relativized and positive separations of [delta sub 2 super p] and [fi sub 2 super p] 

      Lozano Bojados, Antoni; Torán Romero, Jacobo (1989)
      External research report
      Open Access
    • Self-reducible sets of small density 

      Lozano Bojados, Antoni; Torán Romero, Jacobo (1989-11)
      External research report
      Open Access
      We study the complexity of sets that are at the same time self-reducible and sparse or m-reducible to sparse sets. We show that sets of this kind are low for the complexity clases [delta sub 2 super p], [fi sub 2 super p], ...
    • Structural properties of the counting hierarchies 

      Torán Romero, Jacobo (1988)
      External research report
      Open Access
      We study three different hierarchies related to the notion of counting: the polynomial time counting hierarchy, the hierarchy of counting functions, and the logarithmic time counting hierarchy. We investigate the connections ...
    • The MINSUMCUT problem 

      Díaz Cort, Josep; Gibbons, Alan M.; Paterson, Michael Stewart; Torán Romero, Jacobo (1991-01)
      External research report
      Open Access
      In this paper we first present a sequential linear algorithm for an linear arrangement problem on trees, the MINSUMCUT, and then a 0(log n) time parallel algorithm for the MINSUMCUT on trees, which uses n [super 2]/(log ...
    • Turing machines with few accepting computations 

      Torán Romero, Jacobo; Köbler, Johannes (1988)
      External research report
      Open Access
      In this paper we study complexity classes defined by path-restricted nondeterministic machines. We prove that for every language L in the class Few a polynomial time nondeterministic machine can be constructed which has ...