Algorithm and experiments in testing planar graphs for isomorphism.
Algorithm engineering for optimal graph bipartization.
Algorithmes de plus courts chemins pour traiter des données floues
Algorithmic aspects of bipartite graphs.
Algorithmic aspects of total-subdomination in graphs
Let G = (V,E) be a graph and let k ∈ Z⁺. A total k-subdominating function is a function f: V → {-1,1} such that for at least k vertices v of G, the sum of the function values of f in the open neighborhood of v is positive. The total k-subdomination number of G is the minimum value of f(V) over all total k-subdominating functions f of G where f(V) denotes the sum of the function values assigned to the vertices under f. In this paper, we present a cubic time algorithm to compute the total k-subdomination...
Algorithms 62-64. Graph-theoretic algorithms for sparse matrix transformations
Algorithms for Finding Unitals and Maximal Arcs in Projective Planes of Order 16
The paper has been presented at the International Conference Pioneers of Bulgarian Mathematics, Dedicated to Nikola Obreshkoff and Lubomir Tschakalo ff , Sofia, July, 2006.Two heuristic algorithms (M65 and M52) for finding respectively unitals and maximal arcs in projective planes of order 16 are described. The exact algorithms based on exhaustive search are impractical because of the combinatorial explosion (huge number of combinations to be checked). Algorithms M65 and M52 use unions of orbits...
Algorithms for incremental orthogonal graph drawing in three dimensions.
Algorithms for recognizing bipartite-Helly and bipartite-conformal hypergraphs*, **
A hypergraph is Helly if every family of hyperedges of it, formed by pairwise intersecting hyperedges, has a common vertex. We consider the concepts of bipartite-conformal and (colored) bipartite-Helly hypergraphs. In the same way as conformal hypergraphs and Helly hypergraphs are dual concepts, bipartite-conformal and bipartite-Helly hypergraphs are also dual. They are useful for characterizing biclique matrices and biclique graphs, that is, the...
Algorithms for recognizing bipartite-Helly and bipartite-conformal hypergraphs*, **
A hypergraph is Helly if every family of hyperedges of it, formed by pairwise intersecting hyperedges, has a common vertex. We consider the concepts of bipartite-conformal and (colored) bipartite-Helly hypergraphs. In the same way as conformal hypergraphs and Helly hypergraphs are dual concepts, bipartite-conformal and bipartite-Helly hypergraphs are also dual. They are useful for characterizing biclique matrices and biclique graphs, that is, the...
Algorithms for single link failure recovery and related problems.
Algorithms for the two dimensional bin packing problem with partial conflicts
The two-dimensional bin packing problem is a well-known problem for which several exact and approximation methods were proposed. In real life applications, such as in Hazardous Material transportation, transported items may be partially incompatible, and have to be separated by a safety distance. This complication has not yet been considered in the literature. This paper introduces this extension called the two-dimensional bin packing problem with partial conflicts (2BPPC) which is a 2BP with distance...
Algorithms for the two dimensional bin packing problem with partial conflicts
The two-dimensional bin packing problem is a well-known problem for which several exact and approximation methods were proposed. In real life applications, such as in Hazardous Material transportation, transported items may be partially incompatible, and have to be separated by a safety distance. This complication has not yet been considered in the literature. This paper introduces this extension called the two-dimensional bin packing problem with partial conflicts (2BPPC) which is a 2BP with distance...
Algunos grafos compuestos.
From two graphs G1 and G2 on N1 and N2 vertices respectively, the compound graph G1[G2] on N1N2 vertices is obtained by connecting in some way N2 copies of G1.We present in this paper methods of compounding that result in families of graphs with large number of vertices for given values of the maximum degree ∆ and diameter D.
All graphs in which each pair of distinct vertices has exactly two common neighbors
We find all connected graphs in which any two distinct vertices have exactly two common neighbors, thus solving a problem by B. Zelinka.
All Ramsey numbers for connected graphs of order 9.
All regular multigraphs of even order and high degree are 1-factorable.
All Tight Descriptions of 3-Stars in 3-Polytopes with Girth 5
Lebesgue (1940) proved that every 3-polytope P5 of girth 5 has a path of three vertices of degree 3. Madaras (2004) refined this by showing that every P5 has a 3-vertex with two 3-neighbors and the third neighbor of degree at most 4. This description of 3-stars in P5s is tight in the sense that no its parameter can be strengthened due to the dodecahedron combined with the existence of a P5 in which every 3-vertex has a 4-neighbor. We give another tight description of 3-stars in P5s: there is a vertex...
Almost Abelian regular dessins d'enfants
A regular dessin d'enfant, in this paper, will be a pair (S,β), where S is a closed Riemann surface and β: S → ℂ̂ is a regular branched cover whose branch values are contained in the set {∞,0,1}. Let Aut(S,β) be the group of automorphisms of (S,β), that is, the deck group of β. If Aut(S,β) is Abelian, then it is known that (S,β) can be defined over ℚ. We prove that, if A is an Abelian group and Aut(S,β) ≅ A ⋊ ℤ₂, then (S,β) is also definable over ℚ. Moreover, if A ≅ ℤₙ, then we provide explicitly...
Almost all graphs with 2. 522 edges are not 3-colorable.