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## Independent domination versus weighted independent domination

Independent domination is one of the rare problems for which the complexity of weighted and unweighted versions is known to be different in some classes of graphs. Trying to better understand the gap between the two versions of the problem, in the present paper we prove two complexity results. First, we extend NP-hardness of the weighted version in a certain class to the unweighted case. Second, we strengthen polynomial-time solvability of the unweighted version in the class of P2+P3-free graphs to the weighted case. This result is tight in the sense that both versions are NP-hard in the class of P3+P3-free graphs, i.e. P3+P3 is a minimal graph forbidding of which produces an NP-hard case for both versions of the problem.

The scheduling problem of minimizing total tardiness on a single machine is known to be *NP*-hard in the ordinary sense. In this paper, we consider the special case of the problem when the processing times p_j and the due dates d_j of the jobs are oppositely ordered: p_1 >= p_2>=...>=p_n and d_1.

This proceedings publication is a compilation of selected contributions from the “Third International Conference on the Dynamics of Information Systems” which took place at the University of Florida, Gainesville, February 16–18, 2011. The purpose of this conference was to bring together scientists and engineers from industry, government, and academia in order to exchange new discoveries and results in a broad range of topics relevant to the theory and practice of dynamics of information systems. Dynamics of Information Systems: Mathematical Foundation presents state-of-the art research and is intended for graduate students and researchers interested in some of the most recent discoveries in information theory and dynamical systems. Scientists in other disciplines may also benefit from the applications of new developments to their own area of study.

In this paper we consider the problem of finding a spanning *k*-tree of minimum weight in a complete weighted graph which has a number of applications in designing reliable telecommunication networks. This problem is known to be NP-hard. We propose four effective heuristics: the first heuristic is based on the idea of a well-known Prim's algorithm, the second one is based on a dynamic programming approach, and the other two use the idea of iterative improvement from a starting solution. Preliminary numerical experiment was performed to compare the effectiveness of the proposed algorithms with known heuristics and exact algorithms.

Weighted independent domination is an NP-hard graph problem, which remains computationally intractable in many restricted graph classes. Only few examples of classes are available, where the problem admits polynomial-time solutions. In the present paper, we extend the short list of such classes with two new examples.

Structurally stable (rough) flows on surfaces have only finitely many singularities and nitely many closed orbits, all of which are hyperbolic, and they have no trajectories joining saddle points. The violation of the last property leads to Ω-stable flows on surfaces, which are not structurally stable. However, in the present paper we prove that a topological classication of such flows is also reduced to a combinatorial problem. Our complete topological invariant is a multigraph, and we present a polynomial-time algorithm for the distinction of such graphs up to an isomorphism. We also present a graph criterion for orientability of the ambient manifold and a graph-associated formula for its Euler characteristic. Additionally, we give polynomial-time algorithms for checking the orientability and calculating the characteristic.

A form for an unbiased estimate of the coefficient of determination of a linear regression model is obtained. It is calculated by using a sample from a multivariate normal distribution. This estimate is proposed as an alternative criterion for a choice of regression factors.