On the algorithmic complexity of coloring simple hypergraphs and steiner triple systems

In this paper we establish that decidingt-colorability for a simplek-graph whent≧3,k≧3 is NP-complete. Next, we establish that if there is a polynomial time algorithm for finding the chromatic number of a Steiner Triple system then there exists a polynomial time “approximation” algorithm for the chromatic number of simple 3-graphs. Finally, we show that the existence of such an approximation algorithm would imply that P=NP. Dedicated to Paul Erdős on his seventieth birthday     

A random 1-011-011-01algorithm for depth first search

In this paper we present a fast parallel algorithm for constructing a depth first search tree for an undirected graph. The algorithm is anRNC algorithm, meaning that it is a probabilistic algorithm that runs in polylog time using a polynomial number of processors on aP-RAM. The run time of the algorithm isO(T _MM(n) log³ n), and the number of processors used isP _MM (n) whereT _MM(n) andP _MM(n) are the time and number of processors needed to find a minimum weight perfect matching on ann vertex graph with maximum edge weightn.This research was done while the first author was visiting the Mathematical Research Institute in Berkeley. Research supported in part by NSF grant 8120790.Supported by Air Force Grant AFOSR-85-0203A.     

On the computational complexity of a merge recognition problem

A problem arising from the work of C.A.R. Hoare on parallel programming is that of deciding whether a given string ? is a “merge” of two other given strings σ and τ. We describe a polynomial time algorithm for this problem. This algorithm can easily be extended to check, in polynomial time, whether ? is a merge of any fixed number of strings. The problem for an arbitrary number of strings is shown to be NP-complete and so is unlikely to have a polynomial time algorithm.     

The number of centered forms for a polynomial

A general centered form for polynomials is defined. This centered form is based on the concept of an arrangement of the variables of the polynomial. A formula for the number of arrangements of a term and of a polynomial is given. Some examples are computed showing that even polynomials with moderately many variables may have a very large number of possible centered forms.     

Feedback vertex set on AT-free graphs

We present a polynomial time algorithm to compute a minimum (weight) feedback vertex set for AT-free graphs, and extending this approach we obtain a polynomial time algorithm for graphs of bounded asteroidal number.     

Parametric Integer Programming Algorithm for Bilevel Mixed Integer Programs

We consider discrete bilevel optimization problems where the follower solves an integer program with a fixed number of variables. Using recent results in parametric integer programming, we present polynomial time algorithms for pure and mixed integer bilevel problems. For the mixed integer case where the leader’s variables are continuous, our algorithm also detects whether the infimum cost fails to be attained, a difficulty that has been identified but not directly addressed in the literature. In this case, it yields a “better than fully polynomial time” approximation scheme with running time polynomial in the logarithm of the absolute precision. For the pure integer case where the leader’s variables are integer, and hence optimal solutions are guaranteed to exist, we present an algorithm which runs in polynomial time when the total number of variables is fixed.     

Polynomial time algorithms for some classes of constrained nonconvex quadratic problems

In this paper we consider different classes of noneonvex quadratic problems that can be solved in polynomial time. We present an algorithm for the problem of minimizing the product of two linear functions over a polyhedron P in R ⁿ The complexity of the algorithm depends on the number of vertices of the projection of P onto the R ² space. In the worst-case this algorithm requires an exponential number of steps but its expected computational time complexity is polynomial. In addition, we give a characterization for the number of isolated local minimum areas for problems on this form.

Furthermore, we consider indefinite quadratic problems with variables restricted to be nonnegative. These problems can be solved in polynomial time if the number of negative eigenvalues of the associated symmetric matrix is fixed.     

Coloring Fuzzy Circular Interval Graphs

Computing the weighted coloring number of graphs is a classical topic in combinatorics and graph theory. Recently these problems have again attracted a lot of attention for the class of quasi-line graphs and more specifically fuzzy circular interval graphs.The problem is NP-complete for quasi-line graphs. For the subclass of fuzzy circular interval graphs however, one can compute the weighted coloring number in polynomial time using recent results of Chudnovsky and Ovetsky and of King and Reed. Whether one could actually compute an optimal weighted coloring of a fuzzy circular interval graph in polynomial time however was still open.We provide a combinatorial algorithm that computes weighted colorings and the weighted coloring number for fuzzy circular interval graphs efficiently. The algorithm reduces the problem to the case of circular interval graphs, then making use of an algorithm by Gijswijt to compute integer decompositions.     

On testing the divisibility of lacunary polynomials by cyclotomic polynomials

An algorithm is described that determines whether a given polynomial with integer coefficients has a cyclotomic factor. The algorithm is intended to be used for sparse polynomials given as a sequence of coefficient-exponent pairs. A running analysis shows that, for a fixed number of nonzero terms, the algorithm runs in polynomial time.

     

A Deterministic Strongly Polynomial Algorithm for Matrix Scaling and Approximate Permanents

matrix to within a multiplicative factor of . To this end we develop the first strongly polynomial-time algorithm for matrix scaling –– an important nonlinear optimization problem with many applications. Our work suggests a simple new (slow) polynomial time decision algorithm for bipartite perfect matching, conceptually different from classical approaches. Received October 15, 1998     

A note on vertex orders for stability number

We investigate vertex orders that can be used to obtain maximum stable sets by a simple greedy algorithm in polynomial time in some classes of graphs. We characterize a class of graphs for which the stability number can be obtained by a simple greedy algorithm. This class properly contains previously known classes of graphs for which the stability number can be computed in polynomial time. © 1999 John Wiley & Sons, Inc. J Graph Theory 30: 113–120, 1999     

Counting solutions of polynomial systems via iterated fibrations

The paper introduces a new polynomial to count the solutions of a system of polynomial equations and inequations over an algebraically closed field of characteristic zero based on the triangular decomposition algorithm by J. M. Thomas of the nineteen-thirties. In the special case of projective varieties examples indicate that it is a finer invariant than the Hilbert polynomial. Received: 8 March 2008; Revised: 12 August 2008     

Complexity of solving parametric polynomial systems

In this paper, we present three algorithms: the first one solves zero-dimensional parametric homogeneous polynomial systems within single exponential time in the number n of unknowns; it decomposes the parameter space into a finite number of constructible sets and computes the finite number of solutions by parametric rational representations uniformly in each constructible set. The second algorithm factirizes absolutely multivariate parametic polynomials within single exponential time in n and in the upper bound d on the degree of the factorized polynomials. The third algorithm decomposes algebraic varieties defined by parametric polynomial systems of positive dimension into absolutely irreducible components uniformly in the values of the parameters. The complexity bound for this algorithm is double exponential in n. On the other hand, the lower bound on the complexity of the problem of resolution of parametric polynomial systems is double exponential in n. Bibliography: 72 titles.     

PotLLL: a polynomial time version of LLL with deep insertions

Lattice reduction algorithms have numerous applications in number theory, algebra, as well as in cryptanalysis. The most famous algorithm for lattice reduction is the LLL algorithm. In polynomial time it computes a reduced basis with provable output quality. One early improvement of the LLL algorithm was LLL with deep insertions (DeepLLL). The output of this version of LLL has higher quality in practice but the running time seems to explode. Weaker variants of DeepLLL, where the insertions are restricted to blocks, behave nicely in practice concerning the running time. However no proof of polynomial running time is known. In this paper PotLLL, a new variant of DeepLLL with provably polynomial running time, is presented. We compare the practical behavior of the new algorithm to classical LLL, BKZ as well as blockwise variants of DeepLLL regarding both the output quality and running time.     

Factoring polynomials over finite fields

We propose a new deterministic method of factoring polynomials over finite fields. Assuming the generalized Riemann hypothesis (GRH), we obtain, in polynomial time, the factorization of any polynomial with a bounded number of irreducible factors. Other consequences include a polynomial time algorithm to find a nontrivial factor of any completely splitting even-degree polynomial when a quadratic nonresidue in the field is given.     

On single-machine scheduling without intermediate delays

This paper introduces the non-idling machine constraint where no intermediate idle time between the operations processed by a machine is allowed. In its first part, the paper considers the non-idling single-machine scheduling problem. Complexity aspects are first discussed. The “Earliest Non-Idling” property is then introduced as a sufficient condition so that an algorithm solving the original problem also solves its non-idling variant. Moreover it is shown that preemptive problems do have that property. The critical times of an instance are then introduced and it is shown that when their number is polynomial, as for equal-length jobs, a polynomial algorithm solving the original problem has a polynomial variant solving its non-idling version.     

Forests, colorings and acyclic orientations of the square lattice

There is no known polynomial time algorithm which generates a random forest or counts forests or acyclic orientations in general graphs. On the other hand, there is no technical reason why such algorithms should not exist. These are key questions in the theory of approximately evaluating the Tutte polynomial which in turn contains several other specializations of interest to statistical physics, such as the Ising, Potts, and random cluster models.Here, we consider these problems on the square lattice, which apart from its interest to statistical physics is, as we explain, also a crucial structure in complexity theory. We obtain some asymptotic counting results about these quantities on then ×n section of the square lattice together with some properties of the structure of the random forest. There are, however, many unanswered questions.Supported by a grant from D.G.A.P.A.Supported in part by Esprit Working Group No. 21726, RAND2.     

On submodular function minimization

Earlier work of Bixby, Cunningham, and Topkis is extended to give a combinatorial algorithm for the problem of minimizing a submodular function, for which the amount of work is bounded by a polynomial in the size of the underlying set and the largest function value (not its length). Research partially supported by a grant from the Natural Sciences and Engineering Research Council of Canada.     

Energy decay for Timoshenko systems of memory type

Linear systems of Timoshenko type equations for beams including a memory term are studied. The exponential decay is proved for exponential kernels, while polynomial kernels are shown to lead to a polynomial decay. The optimality of the results is also investigated.     

Parameter choices on Guruswami–Sudan algorithm for polynomial reconstruction

Guruswami–Sudan algorithm for polynomial reconstruction problem plays an important role in the study of error-correcting codes. In this paper, we study new better parameter choices in Guruswami–Sudan algorithm for the polynomial reconstruction problem. As a consequence, our result gives a better upper bound for the number of solutions for the polynomial reconstruction problem comparing with the original algorithm.