Mahdieh Hasheminezhad
Abstract
An edge coloring of a digraph $D$ is called a $P_3$-rainbow edge coloring if the edges of any directed path of $D$ with length 2 are colored with different colors. It is proved that for a $P_3$-rainbow edge coloring of a digraph $D$, at least $\left\lceil{log_2{\chi(D)}} ...
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An edge coloring of a digraph $D$ is called a $P_3$-rainbow edge coloring if the edges of any directed path of $D$ with length 2 are colored with different colors. It is proved that for a $P_3$-rainbow edge coloring of a digraph $D$, at least $\left\lceil{log_2{\chi(D)}} \right\rceil$ colors are necessary and $ 2\left\lceil{log_2{\chi(D)}}\right\rceil\}$ colors are enough. One can determine in linear time if a digraph has a $P_3$-rainbow edge coloring with 1 or 2 colors. In this paper, it is proved that determining that a digraph has a $P_3$-rainbow edge coloring with 3 colors is an NP-complete problem even for planar digraphs. Moreover, it is shown that $\left\lceil{log_2{\chi(D)}}\right\rceil$ colors is necessary and sufficient for a $P_3$-rainbow edge coloringof a transitive orientation digraph $D$.
Mohsen Arab; Mahdieh Hasheminezhad
Abstract
Community detection has a wide variety of applications in different fields such as data mining, social network analysis and so on. Label Propagation Algorithm (LPA) is a simple and fast community detection algorithm, but it has low accuracy. There have been presented some advanced versions ...
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Community detection has a wide variety of applications in different fields such as data mining, social network analysis and so on. Label Propagation Algorithm (LPA) is a simple and fast community detection algorithm, but it has low accuracy. There have been presented some advanced versions of LPA in recent years such as CenLP and WILPAS. In this paper, we present improved versions of CenLP and WILPAS methods called CenLP+ and WILPAS+ respectively. Experiments and benchmarks demonstrate that while CenLP+ is as fast as CenLP, it outperforms CenLP on both synthetic and real-world networks. Moreover, while accuracy of WILPAS+ on synthetic networks comparable with that of WILPAS, on real-world networks, WILPAS+ excels WILPAS. In addition, whereas both presented methods CenLP+ and WILPAS+ show high accuracy on synthetic networks, on real-world networks they outperform remarkably all other tested label propagation based algorithms for community detection. Therefore, since CenLP+ and WILPAS+ are both fast and accurate, specially on real-world networks, they can efficiently reveal community structures of mega-scale social networks.
Mahdieh Hasheminezhad
Abstract
In a pointed conflict-free partial (PCFP) colouring of a digraph, each vertex has at least one in-neighbour with unique colour. In this paper, it is proved that PCFP $k$-colourability of digraphs is NP-complete, for any $k >0$. Nevertheless for ...
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In a pointed conflict-free partial (PCFP) colouring of a digraph, each vertex has at least one in-neighbour with unique colour. In this paper, it is proved that PCFP $k$-colourability of digraphs is NP-complete, for any $k >0$. Nevertheless for paths and cycles, one can in linear time find a PCFP colouring with a minimum number of colours and for a given tree, one can find a PCFP 2-colouring. In this paper a bipartite digraph whose arcs start from the same part is called a one-way bipartite digraph. It is proved every one-way bipartite planar digraph has a PCFP 6-colouring, every one-way bipartite planar digraph whose each vertex has in-degree zero or greater than one, has a PCFP 5-colouring and every one-way bipartite planar digraph whose each vertex has in-degree zero or greater than two, has a PCFP 2-colouring. Two simple algorithms are proposed for finding a PCFP colouring of a given digraph such that the number of colours used is not more than the maximum out-degree of the vertices. For a digraph with a given PCFP colouring, it is shown how to recolour the vertices after vertex or arc insertion or deletion to obtain a PCFP colouring for the new digraph.
