arXiv subjects
Publications and source records attributed to Andras Farago.
We prove the unexpected result that almost uniform sampling of independent sets in graphs is possible via a probabilistic polynomial time algorithm. Note that our sampling algorithm (if correct) has extremely surprising consequences; the most important one being no less than the unlikely collapse NP=RP.
A classic and fundamental result about the decomposition of random sequences into a mixture of simpler ones is de Finetti's Theorem. In its original form it applies to infinite 0-1 valued exchangeable sequences. Later it was extended and generalized in numerous directions. After reviewing this line of development, we present our new decomposition theorem, covering cases that have not been previously considered. We also introduce a novel way of applying these types of results in the analysis of random networks. For self-containment, we provide the introductory exposition in more details than usual, with the intent of making it also accessible to readers who may not be closely familiar with the subject.
Filtering packet traffic and rules of permit/denial of data packets into network nodes are granted by facilitating Access Control Lists (ACL). This paper proposes a procedure of adding a link load threshold value to the access control list rules option, which acts on the basis of threshold value. The ultimate goal of this enhanced ACL is to avoid congestion in targeted subnetworks. The link load threshold value allows to decide that packet traffic is rerouted by the router to avoid congestion, or packet drop happens on the basis of packet priorities. The packet rerouting in case of high traffic loads, based on new packet filtering procedure for congestion avoidance, will result in the reduction of the overall packet drop ratio, and of over-subscription in congested subnetworks.
We present an approach that can be useful when the network or system performance is described by a model that is not Markovian. Although most performance models are based on Markov chains or Markov processes, in some cases the Markov property does not hold. This can occur, for example, when the system exhibits long range dependencies. For such situations, and other non-Markovian cases, our method may provide useful help.
We consider random graphs in which the edges are allowed to be dependent. In our model the edge dependence is quite general, we call it $p$-robust random graph. It means that every edge is present with probability at least $p$, regardless of the presence/absence of other edges. This is more general than independent edges with probability $p$, as we illustrate with examples. Our main result is that for any monotone graph property, the $p$-robust random graph has at least as high probability to have the property as an Erdos-Renyi random graph with edge probability $p$. This is very useful, as it allows the adaptation of many results from classical Erdos-Renyi random graphs to a non-independent setting, as lower bounds.
We introduce a concept of efficiency for which we can prove that it applies to all paddable languages, but still does not conflict with potential worst case intractability. Note that the family of paddable languages apparently includes all known natural NP-complete problems. We call our concept Roughly Polynomial Time (RoughP). A language $L,$ over an at least 2-symbol alphabet, is in RoughP, if the following hold: (1) there exists a bijective encoding $α$ of strings, such that both $α$ and its inverse are computable in polynomial time; (2) there is a polynomial time algorithm $\cal A$, which is an errorless heuristic for $L,$ with exponentially vanishing failure rate relative to the $α$-spheres $S^{(α)}_n=\{α(x)\,|\;\, |x|=n\}$. It means, $\cal A$ always correctly decides whether $x\in L$ or $x\notin L$, whenever it outputs a decision. For some inputs, however, it may not output a decision, rather it may return a special sign, meaning "don't know." But the latter can happen only on an exponentially small fraction of each $α$-sphere. We prove that RoughP contains all paddable languages. This may contribute to the explanation of the often observed gap between practical algorithm performance and theoretical worst case analysis for hard problems. Furthermore, the proof also provides a general method to construct the desired encoding and the errorless heuristic. Additionally, we also show how to use it for efficiently generating large, random, guaranteed positive and negative test instances for any paddable language, including all known natural NP-complete problems. In fact, it appears that every practical decision task (whether in NP or not) can be represented by paddable languages, and, therefore, our RoughP framework applies to all of them. We also explore some connections between RoughP and other complexity classes.