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Search: authors:"Stefan Kiefer"

9 papers found.
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Selective Monitoring

We study selective monitors for labelled Markov chains. Monitors observe the outputs that are generated by a Markov chain during its run, with the goal of identifying runs as correct or faulty. A monitor is selective if it skips observations in order to reduce monitoring overhead. We are interested in monitors that minimize the expected number of observations. We establish an...

On Computing the Total Variation Distance of Hidden Markov Models

We prove results on the decidability and complexity of computing the total variation distance (equivalently, the L_1-distance) of hidden Markov models (equivalently, labelled Markov chains). This distance measures the difference between the distributions on words that two hidden Markov models induce. The main results are: (1) it is undecidable whether the distance is greater than...

Counting Problems for Parikh Images

Given finite-state automata (or context-free grammars) A,B over the same alphabet and a Parikh vector p, we study the complexity of deciding whether the number of words in the language of A with Parikh image p is greater than the number of such words in the language of B. Recently, this problem turned out to be tightly related to the cost problem for weighted Markov chains. We...

On Restricted Nonnegative Matrix Factorization

Nonnegative matrix factorization (NMF) is the problem of decomposing a given nonnegative n*m matrix M into a product of a nonnegative n*d matrix W and a nonnegative d*m matrix H. Restricted NMF requires in addition that the column spaces of M and W coincide. Finding the minimal inner dimension d is known to be NP-hard, both for NMF and restricted NMF. We show that restricted NMF...

Proving the Herman-Protocol Conjecture

optimal. 1998 ACM Subject Classification F.1.2 Modes of Computation ? Full version at http://arxiv.org/abs/1504.01130. ? Stefan Kiefer is supported by a University Research Fellowship of the Royal Society

Bisimilarity of Probabilistic Pushdown Automata

/0340); his short visit at Oxford was also supported by ESF-GAMES grant no. 4513. Stefan Kiefer is supported by the EPSRC. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 In CAV , pages 50 - 61 , 1996 . S. B?hm , S

Stabilization of Branching Queueing Networks

the Czech Science Foundation, grant No. P202/10/1469. Stefan Kiefer is supported by a DAAD postdoctoral fellowship. and phrases continuous-time Markov decision processes; infinite-state systems

Computing Least Fixed Points of Probabilistic Systems of Polynomials

LIPIcs.STACS. COMPUTING LEAST FIXED POINTS OF PROBABILISTIC SYSTEMS OF POLYNOMIALS JAVIER ESPARZA ANDREAS GAISER STEFAN KIEFER We study systems of equations of the form X1 = f1(X1, . . . , Xn

Computing Least Fixed Points of Probabilistic Systems of Polynomials

LIPIcs.STACS. COMPUTING LEAST FIXED POINTS OF PROBABILISTIC SYSTEMS OF POLYNOMIALS JAVIER ESPARZA ANDREAS GAISER STEFAN KIEFER We study systems of equations of the form X1 = f1(X1, . . . , Xn